The Darya Rose Show
Aug. 17, 2021

Sunscreens and sunprotection with Dr. Brian Diffey

Sunscreens and sunprotection with Dr. Brian Diffey

Sunscreen scientist Dr. Brian Diffey describes the safety and effectiveness of different sunscreens, and how to optimize sunscreen use for health and quality of life.

Apple Podcasts podcast player badge
Spotify podcast player badge
Overcast podcast player badge
PocketCasts podcast player badge
Google Podcasts podcast player badge
Amazon Music podcast player badge
Pandora podcast player badge
Stitcher podcast player badge

Brian Diffey, BSc, AKC, PhD, DSc is Emeritus Professor of Photobiology in Dermatological Sciences, Institute of Cellular Medicine at the University of Newcastle, UK.

During his career in the NHS, he established an internationally-respected research program in skin photobiology, particularly in the measurement of personal sun exposure; its effects in normal and diseased human skin; and ways to minimize excessive exposure, especially through the use of topical sunscreens.

He has advised a number of bodies on sun exposure and skin health including the World Health Organization, Department of Health, and the Cancer Research UK SunSmart program, as well as patient support groups concerned with sun-related diseases such as melanoma, vitiligo and xeroderma pigmentosum.

He invented both the UVA Star Rating for sunscreens in conjunction with Boots in the UK, and the Critical Wavelength adopted by the Food & Drug Administration in the USA as the sole measure of broad spectrum protection.

In 1999 he was awarded the Medal of the Society of Cosmetic Scientists for his contributions to suncare, and in 2011 was honoured at the International Sun Protection Conference for significant innovation in the field of photoprotection.

He is an honorary member of the British Association of Dermatologists, the Swedish Society for Dermatology and Venereology, and the European Society for Photodermatology.



Human safety review of "nano" titanium dioxide and zinc oxide

Current Highlights About the Safety of Inorganic Nanomaterials in Healthcare

Review of environmental effects of oxybenzone and other sunscreen active ingredients

FDA Trials Find Sunscreen Ingredients in Blood, but Risk Is Uncertain

Update About the Effects of the Sunscreen Ingredients Oxybenzone and Octinoxate on Humans and the Environment

Hawaii and Other Jurisdictions Ban Oxybenzone or Octinoxate Sunscreens Based on the Confirmed Adverse Environmental Effects of Sunscreen Ingredients on Aquatic Environments

Non-sunscreen photoprotection: antioxidants add value to a sunscreen

Optimal sunscreen use, during a sun holiday with a very high ultraviolet index, allows vitamin D synthesis without sunburn

The effect of sunscreen on vitamin D: a review

Sunscreen recall: What the finding of a cancer-causing chemical means for you

Current principles of sunscreen use in children


Environmental Working Group’s guide to sunscreen


Darya's favorite all around sunscreen for outdoor activities: iS Clinical Eclipse SPF 50+ (this stuff is magic)

Darya's favorite daily face sunscreen: Josh Rosebrook's Nutrient Day Cream

Darya's favorite backup sunscreen for face and body: Rhonda Allison Daytime Defense SPF 30

Notice: Any purchases made through my links to Amazon will result in them sending us a few cents that will certainly not cover the cost of running this show.


Darya Rose: [00:00:00] I'm Dr. Darya Rose, and you're listening to The Darya Rose Show, where we bring a fact-based perspective to answer all those confounding questions that come up in our day-to-day lives. From achieving optimal health, to making conscious choices about your purchases, and raising kids that thrive, we are here to help you navigate your life with confidence.

Hello, and welcome back to The Darya Rose Show. Before we get started, I wanna let you know that this will actually be the last episode for Season one of the show. I'm going to take a break for a few weeks, and I will be returning in the fall with season two. Don't worry, I promise, I will not be gone for that long. Today, we will be talking about sunscreen, including how they work, how to choose one, and best practices for preventing sunburn, skin cancer and aging.

Dr. Brian Diffey is Emeritus Professor of Photobiology in Dermatological Sciences, Institute of Cellular Medicine at the University of Newcastle, in the [00:01:00] UK. During his career in the NHS, he established an internationally respected research program in skin photobiology, particularly in the measurement of personal sun exposure, its effects in normal and disease human skin, and ways to minimize excessive exposure, especially through the use of topical sunscreens. He has advised a number of bodies on sun exposure and skin health, including the World Health Organization, the Department of Health, and the Cancer Research UK SunSmart program, as well as patient support groups concerned with sun-related diseases such as melanoma, vitiligo, and xeroderma pigmentosum.

He invented both the UVA Star Rating system for sunscreens in conjunction with Boots in the UK, and the Critical Wavelength adopted by the Food & Drug Administration in the USA as the sole measure of broad-spectrum protection. In 1999, he was awarded the Medal of the Society of Cosmetic Scientists for his contributions to suncare. And in 2011 was honored at the [00:02:00] International Sun Protection Conference for significant innovation in the field of photoprotection. He has an honorary member of the British Association of Dermatologists, the Swedish Society for Dermatology and Venereology, and the European Society for Photodermatology.

I learned so much from Brian, and actually feel a lot better about using a lot of the common and sunscreens on the market. And since I know you're curious, I will include links to the sunscreen I personally use in the show notes. Thank you so much for listening, and I hope you enjoy this episode. Brian Diffey, welcome to the show.

Brian Diffey: Hi.

Darya Rose: I'm really excited to talk to you about this. I have been, uh, reading about and researching sunscreen for a long time, and I find this very confusing. You know, I'm, I'm a trained scientist, so I'm not completely ignorant about biology or anything like that, but I feel like the science changes a lot. And also the technology seems to have changed quite a bit over the last decade or so. So I'm just really excited to talk to you [00:03:00] and get your take on how we should be behaving in the sun.

Brian Diffey: Okay.

Darya Rose: Let's just kind of start with the basics. With sun protection, what really are our goals when we're thinking about sunscreen and sun protection?

Brian Diffey: Let's, let's start right at the beginning. What do we know? Well, we've got overwhelming evidence that when we expose ourselves to the sun's ultraviolet or UV rays, this is a major factor in human skincare. But if we want to manage our risk of skincare, so we don't necessarily need to keep out of the sun. I mean, for example, if you go with your family to the beach on a summer's day, you're making the choice not to minimize your risk of skin cancer, but rather, just we sort of faced it since... embraced it as part of an attempt for you to enjoy your life and your quality of life.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: And so I- I've looked at a pragmatic approach, I think, then is to adopt strategies that control our exposure to the sun, commensurate with our need or [00:04:00] desire to be out of doors. And the approach we adopt to limit our exposure is what we call sun protection or photoprotection. Now, you say that, that sudden, of course, sunburn, yes, it causes other things as well as skin aging, and skin cancer. But I guess sunburn and skin cancer are the two, two mechanisms that people are most concerned about. Are they the same. Well, no, they're not. I mean, the mechanisms leading to sunburn from too much sun exposure are different from those that increase our risk of skin cancer.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: Now, Sunburn is an acute effect. And what I mean by that is it appears within hours of sun exposure, and normally resolves within a few days. Basically, what happens is that the sun's UV rays enter to the upper layer of our skin, and this is known as the epidermis. And there, interacts with cells in causes the release of substances like cytokines that diffuse to the lower layer [00:05:00] of the skin. And that's the dermis, which is where the blood vessels, uh, reside. There are no blood vessels in the epidermis. And what happens is that these cytokines and other chemicals cause the blood vessels to dilate. Now, when a blood vessel dilates, more blood flows through it, and this is what we perceive as a red skin, when we got sunburned.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: But turning to skin cancer, this is a chronic effect. And it's a chronic effect because it results not just from a few hours of sun exposure, but from decades of sun exposure. And because of that, it's mostly a disease of the elderly. And although it can happen, it is incredibly rare in childhood.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: What happens is that if a photon of the UV enters the epidermis, it can damage the DNA and ourselves there. Now this damage is almost always repaired. But sometimes the repair isn't perfect, and [00:06:00] we get, which, you, you know are called mutations. But most mutations in the skin are harmless. But if a mutation happens in a gene that controls cell growth, for example, the p53 gene, that can cause your, uh, skin cells to start dividing uncontrollably. And this is really the first step in the stage to skin cancer.

Darya Rose: So really it's a numbers game? Like, the older you get, the more likely you're to accumulate these mutations. And one of them... One of them might become cancerous?

Brian Diffey: Absolutely. Yes, you've got it.

Darya Rose: So I, I have a question about the, the sunburn mechanism. Then I didn't realize it was the, the blood vessels dilating. Why does it hurt to touch?

Brian Diffey: Well, what it hurts to touch is that when the sunburn, um, is severe, you can get swelling or blistering or a derma. And that pressure of the swelling of the skin, the blistering, touches on the nerve endings. And this is when it's painful. Sunburn is only really [00:07:00] painful to touch when you've got a severe sunburn. When you, you know, you, you, by the time you go to bed that evening, your skin is looking like a lobster red. And a mild sunburn isn't painful. It's when it gets severe and it's accompanied by a blustering, which is derma.

Darya Rose: That... I, I see. So, I mean, I think... I mean, as a 40 something female, [laughs] I actually am quite concerned about skin aging as well. Is that... Uh, what's the mechanism that happens in that case?

Brian Diffey: Well, the skin aging, the, the damage as occurring in the deeper layer of the skin in the dermis, we have substances like collagen, which again, over many years, over decades, can be disrupted by UV exposure. That leads to changes, which we perceive as a leathery skin, wrinkles, sagging, pigmentary changes in the skin. And while we're fairly confident that the sun is related to skin aging, is that it's... If you look at, [00:08:00] um, ordinary people say the face of elderly people or the backs of their hands, they can look quite wrinkled and sacking. But if you take a look at this parts of their body, such as their lower back, or maybe their buttock feature, hardly ever exposed to the sun, then you see that still retain the elasticity of young skin.

Darya Rose: Oh, interesting. So the UV ha- has direct impact on the collagen in itself. And, and that is what, what causes the aging effect?

Brian Diffey: Well, the collagen and elastin, yes. The, the, the, the, the compounds that gives structure to the skin.

Darya Rose: Got it, got it. So when we start thinking about sun protection then, what are the basic types of sunscreen?

Brian Diffey: Okay. Well, that's... the heart of any sunscreen is the active ingredients, only refer to these as UV absorbers or UV filters. Now, UV filters can be either organic chemicals or inorganic chemicals. Now, the inorganic chemicals I know are often [00:09:00] referred to as physical blockers or mineral sunscreens, but I really prefer to use the term inorganic. You've got organic chemicals on one hand, inorganic chemicals like zinc oxide, and titanium dioxide.

Darya Rose: And I just want to clarify to everybody that we're talking about the chemical word for organic. So that means containing carbon. We're not talking about lacking pesticides or [crosstalk 00:09:20]-

Brian Diffey: Oh, sure. Sure. That, that-

Darya Rose: ... my readers might not know that, so. [laughs]

Brian Diffey: Oh, yeah, absolutely. Yeah. I mean, organic, uh, chemicals, as you know, contain carbon. And inorganic contain any other elements, but carbon.

Darya Rose: Right. Okay. So there's... So the active ingredients are sort of either organic or inorganic. And what are the differences there in terms of like for, for us?

Brian Diffey: Well, there are, I suppose, about 50. Just start a better, there are about 50 or 60 UV filters that are approved by various agencies around the world. Different agencies approve different products, such that in fact, only [00:10:00] 11 of these 50 or 60 have been approved globally. And most of these, in fact, nine of the 11 are organic chemicals. And two of them are inorganic, uh, inorganic chemicals, titanium dioxide, and zinc oxide dioxide. In thinking about sunscreens, it's important to realize that we- we've still remained largely ignorant of the relative importance of different wavelengths or parts of UV spectrum in causing damage like skin cancer and aging of the skin.

And it seems to me that in the absence of this knowledge, then the logical approach, uh, to sun protection is what we should seek to do is to reduce the total exposure on our skin rather than selectively modify the spectrum of UV, which is absorbed by the skin. And so the sensible approach that, that I take to sunscreens is that they should absorb more or [00:11:00] less uniformly throughout the UV spectrum. That is, they should absorb UVB and UVA to much the same extent. And we refer to a sunscreen that exhibits this more or less equal absorption to all wavelength as a broad-spectrum sunscreen. Now, what's the rationale behind this? Well, our skin has evolved for millennia to exist in harmony with the mix of wavelengths that make up spectrum of sunlight on the earth surface.

When we step under a tree to seek natural shade, or, or we wear clothing to protect our skin from UV, both shade and clothing are what we term approximately neutral density filters. In other words, they reduce the total amount or the quantity of sunlight reaching our skin, but hardly change the mix of wavelengths or the quality of the spectrum. And [00:12:00] the benefit of using a broad-spectrum sunscreen, as opposed to perhaps the host- more historic ones which contain just strong UVB absorbers, is that for a given time in the sun, the total UV dose absorbed by the skin is much less than if someone had used, say, for example, a sunscreen with, with the same SPF. And we'll come on to talk about SPF in a moment, I suspect, but absorbing mainly in the UVB spectrum.

Darya Rose: Got it. So earlier you said that we are ignorant of many of the different types of wavelengths. So when you say UVA and UVB, are you... Are those just the known ones, and you're... There are more that we haven't named yet, or are they all included in UVA and UVB?

Brian Diffey: Well, no. I mean, back in 1932, it was decided to split the UV spectrum into three sub bands called UVA, UVB, and UVC. And these are defined by specific wavelength limits. Now, [00:13:00] UVC radiation is the very short wavelength part of UV spectrum. And although it's submitted by the sun, it's absorbed by our atmosphere. So UVC rays don't reach us here on the earth surface, the only sub spectrum of , of UV, which reaches us is UVB, which... And UVA. So when we talk about UVB and UVA together, they make the UV rays that reaches here on the earth surface.

Darya Rose: Got it. And I- I've read that... Well, I for- is it UVB that's associated with sunburn and UVA is more associated with melanoma, or is it about right?

Brian Diffey: Well, well, no. A little bit simplistic. Certainly, I think it's true to say that UVB is largely responsible for sunburn. Of something like 85% of the sunburn from the sun is caused by the UVB rays, is about 15% by UVA rays. Now, when it comes to other effects like melanoma, other types of skin cancer, skin aging, [00:14:00] we really are pretty ignorant. And we shouldn't really pretend that we know very much, as I said earlier on, because we remain largely ignorance of the relative importance of different wavelengths. That's why we should go for broad-spectrum sunscreens. I think these terms that you often hear, it said that UVB causes burging... and burning and UVA causes aging. But I think the only merit of that statement is that burning begins with a B, and aging begins with an A. [laughs]

Really, I think we shouldn't get too hung up on, you know, UVB and UVA 'cause both of them are always present in sunlight. So we can't separate them on the rising of the sun, so in a way what's important is, is the UV from the sun, not worrying too much about whether it's B or A, because they're always there together.

Darya Rose: Got it. So we're looking for a broad-spectrum, sunscreen. What does that... How does that relate to the organic versus inorganic does, does... do we need to have? Both or does one do more than the other? How does that relate?

Brian Diffey: Well, in choosing a [00:15:00] sunscreen, what I would recommend is product often at least an SPF 30 with broad-spectrum protection, for the reasons that, that I've given. And you can achieve this more easily if you have a mix of both organic and inorganic chemicals. Having a sunscreen with just one active filter is, is less effective than if you can mix them. I mean, the, the, the modern sunscreen, certainly we have available here in Europe contain up to five or six active UV filters. And by mixing them together in different proportions, we can... What manufacturers are aiming to do is to arrive at a, uh, a UV absorption spectrum, which is more or less flat throughout the UV spectrum. But equally as important as choosing all the mix of filters you're going to use is the acetic properties or the feel of a sunscreen.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: Now, a product where the very high SPF is really of little [00:16:00] use if you use it only once because you don't like it, or you find it so unpleasant that... to use that what you do is to compensate by only applying a very small amounts. I've seen people take an SPF 50, which can be sometimes a little bit thick. And they don't like it. They just put a little bit on. Now, what we need to remember is that the protection we get from the sunscreen isn't just related to the label, SPF on the front of the bottle, but also onto how generously apply it. So actually, you, you often find that applying an SPF 20 product, which contains a little bit more water, and so it's a little bit easier to spread than SPF 50. And actually end up with giving you better protection.

The problem with taking a product with just one active ingredient, for example, zinc oxide, is that you won't achieve the high protection that balance broad-spectrum protection that you would if you could take... Uh, if you use products containing a mixture of organic and inorganic filters. And certainly, [00:17:00] you'll find that they're probably not as quite so cosmetically, um, appealing as sunscreen with a mix of filters.

Darya Rose: So I definitely have sunscreens that I use and enjoy [laughs]-

Brian Diffey: Yep.

Darya Rose: ... that are... That contain zinc oxide and titanium oxide, or do they kind of cover the same spectrum, and the inorganics covered different spectrums?

Brian Diffey: No, no. What you'll find is that they'll, they'll refer to the broad-spectrum, but certainly with titanium dioxide, you won't get very flat absorption across the UV spectrum. Titanium dioxide absorbs much more strongly in the shorter UV wavelengths than the longer UV wavelengths. And so, uh, the reason why certainly with European sunscreens, you'll find that nearly all of them will contain organic chemicals as well, is you'll get a much more balanced absorption spectrum or broad-spectrum protection. So just because something is called broad-spectrum protection, it may have passed the threshold for defining [00:18:00] broad-spectrum protection, but it actually won't be quite as good as sunscreens containing a mixture. And actually, because of this, that's why that there's good reason to suppose that European sunscreens do offer better broad-spectrum protection than you combine the US.

Darya Rose: Oh, that's super interesting. So I, I have read that. And I... My understanding is that one of the reasons is that the FDA has not approved nearly the number of organic, uh, sunscreens as the EU, is that, is that right?

Brian Diffey: Yeah. I mean that, that's true that... I mean, Americans have fewer choices and poor protection than Europeans do from certainly the UVA rays in their sunscreen options.

Darya Rose: I- it's super interesting. I feel like the US is usually more strig- or less stringent with chemicals than the EU. But then, in this case, it seems to be reversed.

Brian Diffey: Oh, so... It's certainly the reverse. Uh, I, I mean, I know of companies, European companies that have been trying to get their modern UV filters into [00:19:00] the US for many years, so far with- without success. And because of this, it means that although US sunscreens will prevent sunburn effectively, generally, they're certainly not as good as European sunscreens that providing balanced. And I want to stress the word balanced full spectrum protection. And what this means is that for a given SPF, that UV sunscreens will let through more UVA to the skin than European product. So if you use an American SPF 30 sunscreen, you'll get a higher dose for most products of UVA to the skin, than you will do it if you use a European SPF rated 30 sunscreen.

Darya Rose: That is fascinating. So I'm... I did a little bit of research on this with the FDA. And one of the things that I found is that they have only recognized the two mineral sunscreen ingredients, so, zinc oxide and titanium dioxide as safe and effective, and the other ones they seem to be more questionable about. Do you happen to know why [00:20:00] that would be? Are they less safe?

Brian Diffey: Well, certainly, the FDA conducted a study and they published in 2019, and found that the application of, uh, at that time, I think it was four commercially available sunscreens that you have in the US under maximal... and I'm stressing this. By maximal use conditions resulted in plus plasma concentrations that gave a little bit, of course, for the concern.

Darya Rose: So the sunscreen was getting into blood?

Brian Diffey: Yeah. But, but it's important to note that in this study, each participant applied the equivalent of two standard bottles of sunscreen over four days. [laughs] Now, this is absolutely greater than typical use, which is that people who use sunscreen go through about one bottle per person per year.

Darya Rose: Right.

Brian Diffey: So what it means is that under typical usage, [00:21:00] this would mean the action for three of the four agents study, I can't remember which ones they were, the levels of active ingredients found in the plasma during typical usage, will certainly fall below, um, the threshold level. And even at maximum usage, which, you, you know, I would think virtually nobody would ever use them like that. Any theoretical risk is almost certainly far smaller than the reduced risk of skin cancer that's been shown to be associated with sunscreen use. And so I would agree with the authors of they FDA who wrote up this study, who said in their paper that these results didn't indicate that we should stop using sunscreen. They just highlighted that, you know, if you, if you slather on loads and loads of sunscreen, then some of the active ingredients can be found in the plus plasma. Whether or not those are actually harmful to human health remains to be seen.

Darya Rose: [00:22:00] I can understand though why people would not really feel comfortable with sunscreen in their blood, especially... I mean, I don't use... I don't go out in the sun every single day, and I don't put sunscreen on my body every single day. But even in the winter time, I always apply some kind of sunscreen to my face. So it is something I'm using daily. So I don't know-

Brian Diffey: Yeah.

Darya Rose: ... the one I use for my face is just think and say [laughs]-

Brian Diffey: Well, you know, don't kid yourself that, that's safe. I mean-

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: When zinc oxide is used in the sunscreen, it's used in the form of very small particles. And these are known as nano-particles, which what that means is that their less than 100 nanometers in size. Now, the reason that nano-particles are used as sunscreens is to achieve better UV... Tenuation of UV radiation, coupled with minimal whitening all the skin. And you can a-

Darya Rose: This is a new technology, right? There, there... When it was sticky, like sort of in the '80s and '90s, when the sunscreen was zinc, it was just like sticky white paste. And now it's smooth and easy to apply.

Brian Diffey: That's right. I mean, it used to be, um, what's called [00:23:00] pigmentary grade zinc oxide. And you find that in cream, for things like diaper rash or nappy rashes, as we say over here, which, which are much bigger particles of, of zinc oxide. But it seems that the jury is still out on the safety of nano-particles of inorganic sunscreen filters like-

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: ... zinc oxide and titanium dioxide. A review that was published in two thousan- let me just see, 2010 now, I think, yeah, concluded that based on the weight of evidence then of all the available data, the risk from the use of nano-particles and sunscreens was considered negligible, but a more recent study published in 2019 from Italy suggested, uh, that the use of these materials might, and I stress the word might, possibly represent a risk for health. So, you know, I guess there's no such thing as a free lunch.

Darya Rose: [laughs] I agree.

Brian Diffey: And you, you, you know, certainly, [00:24:00] zinc oxide is, is probably pretty safe, but to say that it's absolutely safe without risk to health, well, as I say, the jury still had eyes on that question.

Darya Rose: And my understanding is one of the... one of the reasons is that when the zinc particles aren't nano... Turned into nano-particles, they actually can penetrate the skin more than-

Brian Diffey: Exactly. They penetrate skin and, and end up in the blood in the same way as organic chemicals.

Darya Rose: Got it. Okay. Well, [laughs] so if you want the pretty sunscreen, you have to take some risks, it sounds like.

Brian Diffey: Well, yeah. But yeah, of course. I mean, anything you do in life is a risk, isn't it?

Darya Rose: Sure.

Brian Diffey: And you, you know, if you don't use sunscreen sensibly, there's the risk of certainly the short term of getting a painful sunburn, which can spoil your holiday, or your day out, or in the long-term maybe, you know, sunscreens, you know, there is some evidence that they will reduce the risk of skin cancer.

Darya Rose: Right. All right. Well, then let's talk a little bit about SPF because I've [00:25:00] read a lot of conflicting [laughs] stories about this as well.

Brian Diffey: Yeah.

Darya Rose: So can you just talk about what SPF is and how it's determined?

Brian Diffey: Okay. Right. Well, the SPF, it stands for Sun Protection Factor. And if you ask most people, those who think they know what it means, would tell you that it is how much longer skin covered with sunscreen takes to burn compared with skin which doesn't have sunscreen or unprotected skin. So let's suppose you burn after 10 minutes exposure of sunlight, then using a sunscreen labeled with a SPF 15 means that you can remain in the sun for 10 times 15. That's 150 minutes, so two and a half hours before burning.

So how do we determine the SPF? Well, it's the three day procedure. And this is what manufacturers do, uh, when they, uh, want to know the SPF of a new product. [00:26:00] On day one, they get a volunteer, they mark, um, sites on the... usually almost always on the back of the volunteer, probably five-

Darya Rose: Like a real-life person?

Brian Diffey: Oh, oh yeah. Sure.

Darya Rose: Okay.

Brian Diffey: A, a real-life person. Yeah. Yeah. A real-life person. And almost always, it'll be someone with white skin-

Darya Rose: And that's a white person, yeah.

Brian Diffey: A white person. And also a person who will sunburn fairly easily.

Darya Rose: Okay.

Brian Diffey: The reason for that is it takes less UV exposed to go red. So what they do is they mark out these spots on the back of these sites on the back, and then they'll give a series of increasing UV exposure to each of the test sites.

Darya Rose: My goodness.

Brian Diffey: Then the volunteer goes, goes home, and they come back 24 hours later or so on day two. And then the operator then looks at the sites that he's given the exposure to on the back, and notes that site, which produces a just, just perceptible reddening of the skin within the test site. [00:27:00] In other words, what's known as, as a minimal erythema dose, or I mean, erythema is the clinic- clinical name for sunburn. So it's just that dose of UV that he gave, which caused a very slight red, Minimal erythema. And we call this the MED, the Minimal Erythema Dose. Having done that he marks another set of sites, uh, probably on the other side of the back and then apply sunscreen at an internationally agreed thickness of two milligrams of sunscreen per square centimeters of skin.

Darya Rose: Sounds like a lot.

Brian Diffey: Um, well, well, it is a lot. I mean, that's, that's, what's been agreed internationally.

Darya Rose: Okay.

Brian Diffey: So wait 15 to 30 minutes for the sunscreen to dry. And then he does just what he did on day one, which is to give a series of increasing UV exposure. This volunteer goes home and comes back on day three. And then [00:28:00] the operator looks again at the sites that have had the sunscreen on and he notes the MED on the sunscreen protected sites. And the SPF is then... if the MED on the sunscreen protected sites was, shall we say a hundred UV units. It doesn't matter what the units are. And on the unprotected skin, it was say 10 MED... 10 UV units. Then the SPF is a hundred units divided by 10 units, which equals 10. So he'll say the SPF of this product is 10. So that's how, uh, the SPF is determined, but it won't just be in one volunteer. It's nearly in a panel of say, 20 volunteers.

Darya Rose: Okay. I was, I was really going to be astounded. I was like this sound so variable. I mean, yeah, if you just had one person, it seems like you would have-

Brian Diffey: Well, you're right. And, in fact, you, you, [00:29:00] you, you hit the nail on the head there. It's variable because human skin varies from one person to another.

Darya Rose: Like a lot.

Brian Diffey: When, when you take a, say sunscreen of, of nominal Celeste per SPF 25, and you've got your 20 volunteers, then the actual SPF that you can measure might vary anything between 15 to 40. So even though the average by... we're okay to say 25 in any one individual, they might have an SPF 15. And in the next person, it might be 35 or 40. So the SPF at best is just a crude guide to how... to the effectiveness of products in a population of users. It doesn't mean that you'll get the SPF 25. You may get an SPF of 30. And I don't know, your husband might get an SPF at 20, but you're both using the same product at the [00:30:00] same thickness.

Darya Rose: I am just astounded by this. And I really hope they find those people.

Brian Diffey: Yeah. And that cost is under the Borat very controlled conditions. And the reason for this is that the topology or the surface markings of skin vary from one person to another. And they vary across body sites and they vary with age and all sorts of things. So it's not surprising that because if you look at it under a magnifying glass, you'll see different grooves on the skin and they'll vary from one person to another. Now, what I've said is that you might get a variation between say 50 to 35 to 40 for a nominal, less SPF 25. Now you might think that's bad enough. But the... when we say the SPF is 25, this is only true if everybody is applying or an average of 25 is everybody's applying sunscreen at two milligrams per square centimeter. But this [00:31:00] rarely happens in practice because people prefer to apply sunscreen much less than this than the manufacturer is using the testing procedure.

And so the result of this is that most of us are typically protected to a level, which is roughly about one third of what it says on the bottle. So if you apply, say an SPF 30 rated product in the way that most people do, you can probably expect to be protected by, I don't know, round about tenfold. So SPF at best I can... I think you should think of them simply as a ranking system, such that an SPF label, 40 or 50 will give applied in the way you like to apply. It will give you higher protection than an SPF rated labels, 20 or 25, but you won't really be getting 40 or 50 or 20 or 25. You could... [00:32:00] really it depends how much you've put on and what your skin surface like and all the rest of it.

Darya Rose: Wow. That seems... so it sounds like you just want to have whatever works for you to not burn.

Brian Diffey: Sure. That, that, that, that's right. I mean, if you've been out in the sun and doing whatever you've done that day and taken whatever steps you've taken to try to protect your skin, if by the time you go to bed that evening your skin hasn't turned pink, then I think you can be pretty confident that you have over done it in the sun. Sun burn is really feeling like nature's dosimeter or docent- or way of telling us when we've had too much of anything.

Darya Rose: Right. Good example. Some objective way to tell. I'm curious. So I've read in... based on what you're saying, it doesn't sound right, but I've read that anything over SPF 30 or SPF 50 is kind of like all the same. Like it's not that much more protection and that sounds like that's not true.

Brian Diffey: [00:33:00] Well, that's absolutely not true. It's one of the myths that are banned in the sunscreen literature. It really is untrue. Let me explain to you why. Now the basis of this argument is that an SPF, let's say 15 means that one minus a 15th, which is about 93% of sun's UV rays it's absorbed by the sunscreen. And if you take an SPF 30, it means that one minus a 30th, which is about 97% is absorbed. Now you might say, well, there's not much difference between 93% and 97%. And it's... so it's so small that it's a little benefit. So it doesn't really matter whether I use a 15 or a 30. And if we were to use a 50, for example, it would actually come out to be about 98%. But what's important to your skin is not, what's been absorbed by the sunscreen, but how much [00:34:00] UV reaches your skin.

So in the case of an SPF 15 product, the skin exposure relative to unprotected skin for a given time in the sun is one 15th. Or it comes out to be 6.7%. But for an SPF 30 relative exposure is one 30th. That's one over 30, which is 3.3%. In other words, twice as much UV reaches the skin when an SPF 15 product is applied, than when the same quantity of an SPF 30 is applied. So this stupid myth that abide, it doesn't make much difference. It's is so untrue that it leaves me speechless. It's not what the sunscreen's absorbing, who cares what's in the sunscreen. What you care about is what's reaching your skin.

Darya Rose: Yeah, and that's, that's been publicized everywhere. Yeah, that's disappointing. So I was going to [00:35:00] ask... so in that case, like based on what you just said, it sounds like the SPF only measures sunburn potential, not, not broad-spectrum.

Brian Diffey: That's right. That's right. The SPF, I mean, the very nature of the test is it's a sunburn test. It's measuring how effective the product is, in other how much more UV radiation you need with a product on to cause a sunburn than you do without the product.

Darya Rose: So it just sounds like this is going to be a rough estimate for how much active ingredient is in the bottle.

Brian Diffey: That's right, yes.

Darya Rose: Okay [laughs].

Brian Diffey: By, by in large, the way you increase the SPF of a product is by increasing the concentration of the active ingredients, the higher the concentration, obviously the more UV rays are absorbed the product and the higher will be the SPF.

Darya Rose: So earlier we talked about how the difference between sort of the organic [00:36:00] give... can give you a more broad-spectrum versus mineral, or is there some sort of general rule for which of those active ingredients give you a higher SPF? For example, is one way to get a high SPF to just put a lot of zinc in there.?

Brian Diffey: What you want is sunscreens... the best sunscreens that will deliver a high combination of SPF or a combination of a higher SPF with broad-spectrum in a cosmetically appealing product. That's one that you like to use, best achieve from sunscreens containing a mixture of separate organic and inorganic filters. So if you want sunscreen, which is pleasurable to use, then, you know, sticking just to one with zinc oxide in. I mean, I wouldn't do that personally. I would prefer to use one where the manufacturers have got the best mixed in order to achieve broad-spectrum. And they've [00:37:00] also used a formulation, which gives me a product, which is pleasurable to put on that dries quickly on the skin. Doesn't leave a greasy feel, and so on.

Darya Rose: Right. And that's always been the challenge.

Brian Diffey: That's been the challenge, but sunscreens are getting better. Yeah. I mean, certainly sunscreens, which contain high concentrations in zinc oxide in my opinion, aren't very nice to use.

Darya Rose: Yeah.

Brian Diffey: I don't find them very pleasant to use.

Darya Rose: I have a new one that's actually quite, quite lovely.

Brian Diffey: Well, if you like it that's fine. You know, we're all different, but you know, you won't be using the optimum broad-spectrum type of sunscreen with it, but that's, you know, it's a personal choice.

Darya Rose: Right. Sure. And speaking of oxybenz- oxybenzone, I've definitely read that. It seems to be linked to some negative outcomes in the coral reefs and [00:38:00] potentially humans. That's the only sunscreen ingredient that I could find any really negative science about. Does that matter or--

Brian Diffey: Well, I mean, certainly if we look at damage to coral reefs. I mean that there has been in recent times, certainly increased in the public, some scientific interest regarding the impact of organic UV filters like oxybenzone that you mentioned on coral reefs. Now sunscreens can enter the sea in different ways. By first of all, obviously swimmers who have applied sunscreen, or it can occur in wastewater or in land... runoff of water from land. Now there've been a number of scientific studies and who've reports to the press... It's not oxybenzone, but up to 14 different organic UV filters, but all of these are very low concentration in seawater near coral reefs. Now I think it would only be fair to say that with... at the moment with the [00:39:00] currently limited evidence... There is currently limited evidence, I think that suggests that corals are being adversely affected by environmental exposure to UV filters.

But I mean, there are gaps in our knowledge and I guess these needs to be addressed by further studies so that we do have more confident data in which decision makers can make what we might call evidence-based decisions of what to do about coral reefs. I mean, if you're concerned about, you know, sunscreens in coral reefs, then maybe the thing to do is if you're swimming in an area where there are coal Reefs is to perhaps not use sunscreens when, when you're going swimming or, you know, choose to use the sunscreen with say just titanium oxide or zinc oxide in it, which may be, but I mean, I, I'm not aware of any evidence in the country, but that doesn't mean it won't happen that, that, that may be less damaging. But I think at the moment, from [00:40:00] a realistic point of view, I'm not aware of any studies which have actually shown that coral reefs are being adversely affected. I think it's more to do with other things like temperature rises due to global warming and sea water.

Darya Rose: Right. I heard that, that's a much bigger factor in the coral reefs, but just for the record, the, the... well Hawaii and a few other locations have banned oxybenzone and octinoxate, octino-- how do you say that? Octinoxate?

Brian Diffey: They found oxybenzone, I wasn't aware of others but I mean-

Darya Rose: Yeah, it's Octino- octinoxate.

Brian Diffey: Octinoxate.

Darya Rose: Octinoxate.

Brian Diffey: All right. Okay. Yeah. Sure.

Darya Rose: And I'll link to these in the show notes, everyone.

Brian Diffey: But of course were most people swim, I mean, certainly here around the UK. I mean, we don't, you know... coral reefs aren't an issue, so.

Darya Rose: Right. Right.

Brian Diffey: You, you know, if you [inaudible 00:40:47] near coral reefs, you don't have to wear a sunscreen. I mean, put on a wetsuit.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: I mean, that'll give you much, much, much, much better protection than any sunscreen will. And it won't be damaging at all [00:41:00] to, to coral reefs.

Darya Rose: It's a great point.

Brian Diffey: So, so there... So there are ways around it certainly.

Darya Rose: Maybe just a little bit on your face.

Brian Diffey: Well, if you're swimming, you're unlikely to get some burn. Your faces usually face down in the water, isn't it?

Darya Rose: I, I, I, I often swim with my hair up and dry [laughs]. So what about inactive ingredients in sunscreen? Are those, are those relevant very much or is it just cosmetic?

Brian Diffey: Well, I mean, there are different types of [inaudible 00:41:28]. First of all, there's the active ingredients that are just used in the formulation process, that... things like water and glycerin or whatever it might be, just to, you know, ma- make a pleasurable cream. But we also find, now, that some sunscreens contain ingredients like antioxidants and say vitamin C and E, which may enhance the protection of a sunscreen. Now, when we use a sunscreen, if you like conventional photoprotection by sunscreens is entirely passive. And what [00:42:00] I mean by that is that they're designed to attenuate, reduce intensive UV reaching, going into the skin.

But once the UVS gone in, and say DNA damage has occurred, the sunscreen is of no use at all. I mean, it's, it's not working or, or the UV filters cease to work. And so by putting in things like botanical extracts and certain vitamins, these are claimed to provide what you might think of as active photoprotection. In other words, they're set to work by stimulating DNA repair, acting as antioxidants, inhibiting inflammation and, and modulating the immune system. And so it's possible that the addition of these sorts of ingredients to a broad-spectrum sunscreen may further decrease UV-induced damage compared to just the active UV filters alone.

So, you know, there, there may be not a bad thing to have in sunscreens. [00:43:00] Although, uh, I think we should realize that none of these agents like botanical extracts or vitamins and so on provides anything other than just very low to modest photoprotection. And there's certainly no substitute for the UV filters in sunscreen or for other established methods of some protection that we haven't really talked about such as shade or clothing.

Darya Rose: Right. But it is... Is it... you know, it's like these sunscreen companies, they make claims that, that antioxidants or certain vitamins are doing something. So, so it sounds like they may in fact be doing-

Brian Diffey: They, they may. They-

Darya Rose: ... there's just no substitute, no substitute for all these active [crosstalk 00:43:39].

Brian Diffey: No, no. That's right. I mean, they... You know, they, they certainly may well be helping a bit in starting to repair some of the damage that, um, would have been done for those UV photons or rays, which have penetrated the sunscreen there. But just putting an antioxidant on your skin alone without UV filters would be a very poor way [00:44:00] of getting-

Darya Rose: Sounds right. Got it. And while we're on the subject of vitamins, I know that one of the benefits of a human being having their skin in the sun is vitamin D production. How, how does that interact with sunscreen? Is that something we should be concerned about?

Brian Diffey: Well, vitamin D, which we all need for healthy bones, is synthesized. Most of our vitamin D is synthesized in the skin by the action of the sun's UVB rays. And since sunscreens are designed certainly attenuate UVB because UVB, as we spoke about earlier, is major cause for sunburn. You might think that, "Well, if you apply sunscreen, won't it adversely affect this sunburn?" No. People have done studies in the laboratory, and they've shown that if you apply sunscreen at two milligrams per square centimeter, you'll remember, that's the thickness that manufacturers use when they want to determine the SPF. And then you follow this by radiating volunteers with UV lamps. Yes, [00:45:00] it does compromise vitamin D protection. Yeah, sorry, vitamin D production.

But the same effect hasn't seen in real-life for studies. And there are a number of reasons that I think can account for this. Like, as I've already mentioned, people generally apply less quantity of sunscreen than used by manufacturers in the testing process. Typically, manufactur- well, the manufacturer will test a sunscreen at two milligrams a square centimeter. Studies... I have been with people who have done... field studies show that people prefer to apply around about one milligram per square centimeter on average. So they're applying a thinner layer. Also, when a manufacturer tests a sunscreen in the laboratory on the back of a volunteers, he uses a glove finger to spread it nice and uniformly. So he tries to achieve a uniform layer.

But, you know, when you're out and about, and you're putting sunscreen on, you don't see [00:46:00] many people with a glove finger applying their sunscreen. [laughs] They slap it on and they sort of rub it in, in a sort of fairly haphazard way. And so what this means is that some areas of the skin that you think you've applied sunscreen to will have little or no protection. And also, there's some evidence to suggest that only a minority of sunscreen used is actually reapply sunscreen as we're advice to do to maintain adequate sun exposure.

Darya Rose: So you think that the sun is actually getting through, and that's why-

Brian Diffey: Tha- that's right. So that's very interesting. The, the, the, the, the, the, the sun is hitting those areas of skin where there isn't really any little or no sunscreen protection. Secondly, sunscreen is mostly used during recreation exposure, when people plan to remain in the sun for a long period of time. And so, even these areas of skin that are protected, they have only a ce- thin layer of sunscreen on, as we think about it. So that even during this period, adequate UV can penetrate through to the skin to [00:47:00] synthesize clinically significant quantities of vitamin D.

And the last thing to remember is that vitamin D is made in our skin on a daily basis when we're out and about, and not just during a recreational exposure. So that I don't think most people think about applying sunscreen during that casual exposure, such as when you're popping out to the shops at lunchtime during the working week. So I think any apprehension about vitamin D shouldn't be a reason to withhold sunscreen application during extended periods of strong sun exposure or, or sun exposure and strong sunlight.

Darya Rose: Got it. So it sounds like-

Brian Diffey: Ca- can I just... Can I just add one more thing though?

Darya Rose: Yeah, of course.

Brian Diffey: ... which I think actually may be of more concern than recreational sunscreen, is that... I mean, you mentioned you, you, you apply your sunscreen every day throughout the year during the winter. Well, I don't think you'll... that's a very wise thing to do because you know that skincare products, not just recreational sunscreen, but [00:48:00] the moisturizers that people will use, many of these now incorporate UV filters. And so it's possible for protection provided by these products during our casual sun exposure may be sufficient to compromise vitamin D production during the important period of the late summer and early autumn when sun exposure on our skin is important to tal- when the sun is beginning to get weak, it's important to top up our stores of vitamin D which... Our vitamin D stores are in the fats in our, in our body.

And these are, are released during over the winter. Over the winter in certainly the, the northern parts of the US, Canada, UK, the sun is sufficiently weak, that it really doesn't sensitize anything like adequate amounts of vitamin D. So that by being too religious in wanting to block those UV rays when the sun is weak, you actually may be doing more harm than good. So [00:49:00] my advice would be that, you know, come end of September, October when there's still a bit of sunshine around, try to get that bit of sunshine on your skin when you're out and about.

You know, if you're, if you're doing all you can to try to block every last UV photon from your skin, remember that you're not doing your bone health any good.

Darya Rose: Hmm. That's... Thank you. That's good to know. I, I just put it on my face. I'm just mainly concerned about aging. Um, is it not enough UV for... To do any aging damage?

Brian Diffey: Well, are you more concerned about aging your skin than getting osteoporosis later in life?

Darya Rose: Well, so [laughs] so actually I have... I take... That's another thing I was going to mention is that we can... It's also very, very easy to take vitamin D supplements. I actually have... personally, I've talked about this on the show before, I have many mutations. Three out of four that are currently available to test, uh, genetic mutations for being unable to or, or decrease my vitamin D production. [00:50:00] So even when I, um, spend a good amount of time in the sun in southern California, I have my vitamin D levels are like 17, like, really, really clinically low.

Brian Diffey: Oh, really?

Darya Rose: Yeah, so.

Brian Diffey: Oh, okay.

Darya Rose: I take... Every day, I take 6,000 Vitamin D.

Brian Diffey: Oh, that's good.

Darya Rose: And in the winter I take 8,000 [crosstalk 00:50:17].

Brian Diffey: Okay, well, maybe you'll... Um, uh, you're, you're an unusual case. [laughs]

Darya Rose: It's actually not that unusual. It's pretty common for people to have as like a good percentage of the population, like, 20% or something have... or at least in Caucasian people have, have these... at least one or two of these mutations. I have a lot, right.

Brian Diffey: Okay.

Darya Rose: Yeah. Um, but I think... But it's also super easy to get your vitamin D tested these days. You can literally order a kit on Amazon, prick your finger-

Brian Diffey: Sure.

Darya Rose: ... put it on a little blood bank-

Brian Diffey: Yeah.

Darya Rose: ... on a thing and send it in. And they'll tell you your vitamin D.

Brian Diffey: Yeah. But most people will get about 90% of the vitamin D from the sun.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: And about 10% from, from food.

Darya Rose: Okay.

Brian Diffey: Um-

Darya Rose: So it is important to get, to get that sun exposure on-

Brian Diffey: Sure, sure. Yeah.

Darya Rose: ... un- [00:51:00] unprotected skin every once in a while.

Brian Diffey: Yep.

Darya Rose: Great. Um, well, let's talk about the UV index because that's actually something that's been really confusing to me. So we have sunscreen, you have SPF, but I mean, I look at my Apple watch, and it'll tell me the UV index for the day, which is not related to me, it's related to the sky.

Brian Diffey: Yep.

Darya Rose: And in... I've noticed, you know, having used this for several years now, that it doesn't always seem to be correlated with cloud cover or even necessarily the time of year, although a little bit is correlated with that, or even where I am in the earth. I mean, it's, it's super high, for example, in New Zealand. [laughs]

Brian Diffey: Yeah.

Darya Rose: But. Uh, so I'm curious A, like, what, what is determining UVI, If you know? I mean, I know it's not about sunscreen, but if you're... If you would know anything about that, it'd be curious to hear about it.

Brian Diffey: Sure, yeah. Yep.

Darya Rose: And then also, how that relates to how we should think about going in the sun and applying sunscreen at all?

Brian Diffey: Okay. Well, UVI stands for the UV Index. And it's a [00:52:00] measure of the sun burning power of the sun midday. It's solar noon, when the sun is in it's... is going to be this high as that day. So it's... No, actually, it's a factor of the height of the sun in the sky. So the higher the sun in the sky, the higher will be the UV Index for a clear sky. Obviously, when it's cloudy, that would affect the strength of the sun's UV rays reaching the surface. And so the UV Index will be low. So even in the middle of the summer in California, you're in UV Index, whereas, clear day, [inaudible 00:52:33] might go up to, I don't know, 12 or something, maybe not that high 11, 12, but you might find the following day in the summer when it's overcast, the UV Index might be forecast to be only three or four.

So cloud cover makes a difference. But I think... let's talk about... mo most people think that when it's hot, that's when they get sunburned. But of course, that's not true. The, the heat of the sun comes from the sun's infrared rays. And it's the [00:53:00] ultraviolet rays, which course sunburn. But on days during the summer months, when high temperatures are expected, weather forecast will frequently warn about the dangers of high UV. And so it's not surprising that I guess many people think that high ambient air temperatures are a major risk for sunburning.

So although the UV Index is higher on cloudless hot days, compared with cloudy cool days, we shouldn't rely on it. Now, let me try and explain why. During... Say it's a clear, it's cloudless day in the summer. Sunny morning. What happens is that during the morning, both the air temperature and the UV Index would increase steadily until we reach solar noon, Now solar noon is when the sun is at high... is highest in the sky. Now, I'm not sure what, where you are in the States, but over here in the UK at the moment, solar noon occurs at 1:00 PM. That's an hour after [00:54:00] midday, that's because we're on daylight saving time.

In the winter months, solar noon occurs at midday at 12 o'clock. But at solar noon, the UV index has reached its maximum for that day. And after midday, the temperature though, it could generally... in fact, in the summer, temperatures will generally continue to rise. The hottest part of the day in the summer is usually about mid afternoon, 3:00 or 4 o'clock, whereas the UV index is falling after mid day.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: So for example, by late afternoon, the UV index say by 5 o'clock in the afternoon, UV Index may be only one or two and present really no risk of sunburn. And yet, the air temperature might still be in the mid 30s, for example. And so i-it's not uncommon. I've seen people apply sunscreen sitting on... I mean, I live on the coast here in the UK, very close to the beach, and, you know we, we got a hot day, and you'd see people on the beach at 6 o'clock in the evening [00:55:00] when it can be still quite warm, hot, but applying sunscreen, even though the UV index at that time is such that there's no risk of sunburn. And so it's, it's unwise to judge the sun burning power of the sun solely on ambient temperature.

And it's... this is true, not only when it's very hot, but also of course, when it's cloudy, because when it's cloudy, you'll often find that people get sunburned. That is because one, if it's... cloud passes across the sun, the water vapor in the clouds will absorb the infrared rays. They, the warmth which we perceive from the sun. And so you, you feel cool when a cloud passes in front of the sun. But the UV will penetrate through the cloud because UV goes through water. And so, the warming sensation of heat is diminished. When it's very heavy, dark rain clouds, then of course, yeah, they do attenuate the UV a lot.

But light fluffy, white clouds [00:56:00] scattered across the sky make little or no difference to the sun burning power or the strength of the UV rays.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: I think, thinking about numbers, when the UV index is say three or higher, it's wise, I think to start thinking about sun protection, whether it's the limiting your time in the sun, thinking about seeking shade, maybe if you're out in the middle of the day, I don't know, taking a picnic, sitting under a tree, wearing clothing, as well as applying sunscreen, which we've been talking about.

Darya Rose: Brilliant. Uh, that's really fascinating. I didn't know that. So I, I, it sounds like one of the biggest factors is where the sun is in the sky, [crosstalk 00:56:43] more atmosphere, right?

Brian Diffey: When the sun is high in the sky, what happens is that the path length of the sun's rays through the ozone layer, it's the ozone layer is the main factor for absorbing UV is less. And also, when the sun is higher in the sky, a given cone of sunlight [00:57:00] falls on a smaller area of the earth surface. And that means that the intensity of UV rays, the number of UV rays falling per square meter goes up. So both of these factors serve to increase the sun burning power of the sun.

Darya Rose: Very cool. And everybody, if you have... If you're curious what the UVI is where you are today, you can always just... If you have a smartphone, you can usually just ask your smart phone. It'll tell you exactly what it is.

Brian Diffey: Yep.

Darya Rose: Very cool. All right. So above three, we should be wearing UVI... or, sorry.

Brian Diffey: Well, above three, it might be time just to start thinking about it. Obviously-

Darya Rose: Got it.

Brian Diffey: ... if the UV index is nine or 10, then you really should be taking some protection seriously. But if it's three or four, well, just begin to maybe think, "Well, perhaps I won't stay out quite so long or whatever."

Darya Rose: Got it, got it. All right. Well, what about people of color, you know, people with darker skin? I've heard rumors that they, you know, that they have more natural sun protection. I mean, that's not rumor. They have more melanin in their skin than... which is a [00:58:00] more natural sun protection, but I know that that it's also possible for them to get skin cancer. How should people of color think about skin-

Brian Diffey: Well, sure, I mean, you're absolutely right. I mean, people with, with black color of skin, or certainly with black skin, the, the main ingredient or natural biological agent in their skin is, is melanin. It's the, the melanin is come together and what's primary called melanocytes. And the melanocytes in people with dark skin are bigger and more effective sun filters than are people with white skin. And broadly speaking, people with black skin will require something like 10 to 15 times as much UV dose to get a sun burn as people with light-skinned. Now just because dark skinned has some natural protection, it doesn't mean that, you know, you're complete... you're resistant to damage such as things like skin aging... well, skin aging, again is much less than people of color and skin... but skin cancer.

And in countries like the US or, or South Africa, [00:59:00] where people with black and white skin live side by side, the serious type of skin cancer melanoma is about 20 times more common in white Americans than it is in black Americans. And the common sort of skid cancer, which is much less of a concern called basal cell carcinoma or sometimes called [inaudible 00:59:20], it's about 60 times more common, uh, in, in white Americans than it than black Americans.

So because black people, uh, don't sunburn to anything like the same extent is white people, I conducted a survey with colleagues in, in Africa three years ago, and we find that in the UK, um, about two thirds of black people say they didn't ever use any form of sun protection at all. But Africa, it was about one third. So people living in Africa with black skin, more of those think about sun protection than people living in the UK, which is obviously perhaps not surprising 'cause the sun's much stronger.

Darya Rose: Mm-hmm [01:00:00] [affirmative].

Brian Diffey: In black people living in the UK, their chosen form of sun protection was sunscreen. Whereas, in fact, sunscreen was the least popular modality in, in many African countries. And I think that's probably to do with the cost. Sunscreen is quite expensive. And what we found, uh, in, in Africa was that people with black skin chose shade as being the most common form of empty sun exposure. And of course, the reason for choosing shade, it's not only is it free compared to sunscreen, but also shade from the heat of the sun as well. So-

Darya Rose: I imagine also with the... I mean, many of the sunscreens do leave that kind of sticky white. I imagine, that cosmetic factors, I imagine would be more substantial for communities of color.

Brian Diffey: Well, maybe, but again, if you use a sunscreen with a nice mix of organic and inorganic chemicals, which has been formulated by a reputable manufacturer, you won't get sticky white [01:01:00] appearance.

Darya Rose: Okay. So that has improved over the years.

Brian Diffey: Yeah. I think, you know, uh, for those who are enthusiastic zinc oxide, only sunscreens then maybe that's one of the consequences.

Darya Rose: Yeah. And I, I know that there are sunscreens now specifically for people of color. There's something called Black Girl Sunscreen that I think is really popular. [laughs]

Brian Diffey: Yeah. But of course, I mean, there aren't... there aren't in a sense in terms of sunscreens, any different than sunscreens for white people. Maybe it's, more of a marketing thing because a sunscreen to work has to sit on the surface of the skin. It has to bind to the ice layer of the skin called the subcutaneous to work effectively. And so the sunscreen is working if you're like outside the skin, not inside the skin. So the sunscreen itself doesn't really know whether it's protecting black skin or white skin.

Darya Rose: Right. So let's talk then about the best methods for applying sunscreen.

Brian Diffey: Yeah. Well, my tips for applying [01:02:00] sunscreen are to apply it liberally. That's used as much as you feel comfortable to do so to the sides of your skin, where you're going to be exposed 15 to 30 minutes before going into the sun.

Darya Rose: Oh, wow.

Brian Diffey: Um, No, don't... I think a mistake that many people make is, that I've seen people, watched them putting sunscreen. They, they rub it fairly biggest range of their skin. Don't do that. A sunscreen to work properly has to bind to the surface of the skin. And so when you apply sunscreen, spread it lightly over the surface and let it dry. Don't keep rubbing it until it disappears. Because once you force sunscreen down into the skin, it cease to work properly because you wan- it is. It then going down below the layers of the cells that you might want to protect. So just rub it lightly, smoothly over the surface of skin. [laughs] And then-

Darya Rose: I'm picturing myself in my bathroom, like, covered in sunscreen naked and just sort of standing with my arms [01:03:00] out waiting for it to dry.

Brian Diffey: Well, that's, that's that's what you should do-

Darya Rose: Okay.

Brian Diffey: ... because you want the sunscreen to act as a barrier to your skin, not to be inside your skin. And then the next thing is, I suggest you reapply the sunscreen when you've been in the sun for, say, 15 minutes or so.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: So you might ask, "Well, why do I need to reapply, reapply it says to soon?" Now, I'm gonna use an analogy here. And the analogy I'm going to use is if you paint a wall, if you say, go into emotional wall, you often find you, you put on two coats of paint, don't you? Because you put on the first coat, and you might find that some of the original color is showing through still.

Darya Rose: It's uneven, yeah.

Brian Diffey: It's uneven. And whatever. So you wait for it to dry, and then you apply a second coat, and the wall looks much nicer. Well, it's the same with the sunscreen. Earlier on I said that when you look at the skin very closely, you'll see it's... the skin isn't flat. It's composed of a series of ridges and grooves. [01:04:00] And so that when you apply your first layer of sunscreen, and the way that people apply it is [inaudible 01:04:06] finished layer, you may cover the ridges, but you could leave the... Sorry, you may fill the grooves with, with sunscreen, but you'll leave the ridges to be unprotected. So if you then apply a second coat fairly soon after... once the first coat is dried, it's a bit like doing two coats of paint your wall.

You're, you're making... you're then starting to cover the ridges of the skin. And so that you're getting much better protection. So in the same way as you apply two coats of paint to the wall, and it's the same way two coats or sunscreen may be required for adequate, adequate protection. And then of course, it doesn't just end there, that if you're going to do vigorous activity in the sun or you're going to be swimming or touting excessive sweating and rubbing, then, you know, reapplying sunscreen, again, maybe after a couple of hours, it is to be advised.

Darya Rose: [01:05:00] Interesting. So really it's just like a physical barrier on your skin. You just want to-

Brian Diffey: That's, that's-

Darya Rose: ... Like paint.

Brian Diffey: Exactly. If you want to get the best protection for sunscreen, think of it that way. Don't rub it into the skin in the same way as you would do a moisturizer. With a moisturizer, you want to get it into the skin to, to try to prevent water evaporation from the skin. With a sunscreen, you want to bind to the surface of the skin. So if you like... just like this invisible layer, which is attenuating the sun's rays, the sun's UV rays before they reached the skin.

Darya Rose: Fascinating. So what about those sprays sunscreens? That seems to be kind of even. Do those work?

Brian Diffey: Well, yeah. I mean, sunscreens come in all sorts of forms. You get gels, creams, lotions, and you get sprays. Now, you can spray the sunscreen on, but again, it's important, after you're spraying to spread it uniformly and lightly in order to try to create as even a layer as possible as I've just [01:06:00] described.

Darya Rose: Mm-hmm [affirmative]. And I know, I've mentioned benzine and sunscreen earlier. The reason that slipped out of my mouth is because there was a recent recall of a bunch of the sunscreens and they were largely the spray ones-

Brian Diffey: Yeah.

Darya Rose: ... that they were contaminated with benzene. [laughs]

Brian Diffey: Well-

Darya Rose: In the US, yeah.

Brian Diffey: That's right. I mean, I did read about that. And my understanding from what I read was that benzenes, aren't used in sunscreens. And I think the explanation given was that some contamination occurred during the, the manufacturing process. So it's not a fault with a sunscreen per se, but maybe something got in.

Darya Rose: Okay. It was weird.

Brian Diffey: Can I-

Darya Rose: It was, it was a bunch of different brands. Yeah. Go ahead.

Brian Diffey: Yeah. Can I, can I just say one thing that, again, we're thinking about that, you know, you- you'll read that you're often applied to, to apply sunscreen rigorously or generously. And the, the... that... I mean, people, as I've already mentioned, generally apply less than two milligrams per centimeter, which is the thickness used by manufacturers during the testing process. [01:07:00] And, you know, this is... that many people are commentators to... into the trap of believing that consumers apply inadequate amounts of sunscreen. People say, "You're not applying enough sunscreen for sun protection." But my take is the reality is the reverse. People use the quantity. When, when you, as an individual, apply sunscreen, you put on the amount that you feel comfortable with. And so in this sense, you're using the correct tonight for you.

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: Um, and that's generally round about one milligram per square centimeter. That's what you find is correct. I did a, a program with the, the BBC, the British Broadcasting Corporation. That's our main TV channel over here a little while ago, and we got a group of people, and we sort of, if you like, forced them to apply sunscreen at two milligrams per square centimeter. And they hated it. [laughs] Because it was just too much. It was running [01:08:00] off the skin and they didn't like it and so on. And so when we let them apply the amount that they felt comfortable, whether it's, you know, averaging roundabout one milligram per square centimeter.

So the way people, people apply it, they're applying it correctly for them. It's the labeled SPFs that are misleading. Manufacturers are testing their product-

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: At a thickness which doesn't reflect human behavior in order to arrive at an SPF. And so that's what I was saying earlier that divide your SPF by three, and you'll end up with a number which is probably closest to the protection of really get. So it's the SPFs that misleading, not that people are applying sunscreen incorrectly.

Darya Rose: That's an... That's a fantastic point. And it does seem to argue for a using a higher SPF. [laughs]

Brian Diffey: Yeah. That- that's, that's right. At least, by using a higher SPF, uh, you're compensating them for the fact that you're applying it, you know, less than the manufacturer did. And so you're still ending up with an acceptable, [01:09:00] real SPF as opposed to labeled SPF.

Darya Rose: I really appreciate your pragmatism because I- I'm, I'm with you. Like I... For me, it... Quality of life is the most important thing. What's the point of being here if we're not enjoying-

Brian Diffey: Exactly.

Darya Rose: ... enjoying it.

Brian Diffey: Yeah.

Darya Rose: Especially outside. Outside is one of the best places to be.

Brian Diffey: Yeah, that's right. As I started off this interview saying that, you know, minimizing the risk of skin cancer doesn't mean staying out of the sun. It means you, you want to do that, but also enjoy yourself. Life is for enjoying.

Darya Rose: Yeah. I have one last question I wanna, I wanna to ask about children. I think a lot of parents worry about their kids, rightfully. They have, you know, precious little delicate skin-

Brian Diffey: Yeah.

Darya Rose: ... and I've read that it's especially dangerous for young children to get bad sunburns when they're young. But I've also, I've read... I, I couldn't find it again. So it's probably not true, but I've read that, you know, for example, zinc might not be so wonderful for children. I know they do put it in the diaper creams, but [01:10:00] you know, did you have any specific recommendations for kids, or in your opinion, is it just mostly the same?

Brian Diffey: Well, I think the first thing I'd say is that sunscreens is probably best avoided and infants less than six months of age. And the reason I say this is that babies have a higher surface area to body weight ratio compared with older children and adults. And what this means is that a baby's for expo- exposure to the chemicals in sunscreens is, is greater than it would be in an adults. And this possibly increases the risk of an unwanted reaction. And then we haven't spoken about the fact that in some people, sunscreens can cause a contact allergy or-

Darya Rose: Right.

Brian Diffey: ... Photo-contact ecology, which of course irritation on the skin. And so, sunscreens, I think are best avoided in, in, in very... in babies less than six months.

Darya Rose: Keep your infants in the shade. [laughs]

Brian Diffey: Sure. You Keep it... I mean, you don't need to use the sunscreen on a baby, really. You keep them in the shade. You make sure that your baby is wearing loose fitting clothing [01:11:00] that covers the skin and keeps them cool. And obviously, you don't forget a sun hat. I mean, if there's no way to keep your baby out of the sun, then you know, you can apply a small dab of a high SPF sunscreen to a small area, such as the cheeks and the backs of the hands. Um, and I really wouldn't worry about whether it's in based or organic chemical based or whatever, you know, I don't think there's any reason to use one type of sunscreen and even than the other. I think the best thing is, you know, there are plenty of other ways of minimizing the exposure on baby's skin and using a sunscreen.

The sunscreen should actually be your last resort. You should rely more on clothing, loose fitting clothing and shade. And by doing that, you know, there's probably, in most cases, no need to use any sunscreen at all.

Darya Rose: What about older kids like toddlers? I mean, my kids are just always outside, running around. [laughs] It's hard to get them inside.

Brian Diffey: Well, I, I [01:12:00] think the sa- same advice would be for, for anybody. You, you know, if, if their, you know, use, uh, uh, high SPF, broad-spectrum sunscreen, you know, apply it the way I've been talking about, you know, you... I don't think you particularly need to use any particular ingredients in sunscreens for children than you, than you do an adults. I know that, you know, some people prefer to use sunscreens, which are perhaps only inorganic chemicals, like titanium dioxide and zinc oxide, but you know, the safety profile of, I think, all sunscreens made by reputable manufacturers, it's pretty good.

I mean, I would have, I should know, he's growing up, but, you know, I would have no hesitation to, you know applying any sunscreen, sensitively, you know, to children.

Darya Rose: And at this point, I... my understanding is that most of the older sunscreens, I mean, we've been using sunscreens for decades. And most of the older sunscreens-

Brian Diffey: Sure.

Darya Rose: ... that did seem to have a, a poor health profile [01:13:00] have been already kind of removed from the market.

Brian Diffey: Sure, yeah.

Darya Rose: So the ones we're left with are, are pretty solid.

Brian Diffey: Yeah. Yeah, that's right. I mean, things like [inaudible 01:13:08] [benzo Castro 01:13:08], which was the mainstay of sunscreens perhaps 30 years ago-

Darya Rose: The [Peba 01:13:13]?

Brian Diffey: The Peba, that's right.

Darya Rose: Yeah.

Brian Diffey: It is, you know, it's not used now because it would stain clothing, so. And, uh, you know, new UV filters have been developed by manufacturers. And, you know, I think in Europe, which will give really nice balance, broad-spectrum protection, that they have high absorption. So you can achieve high SPFs in a cosmetically appealing product. Yes. Sunscreen, sunscreen just got better over the years.

Darya Rose: That's great to hear. I feel actually a lot more confident [laughs] about all of it after talking to you. So thank you. Um, I was going to ask you, do you have... I mean, you know, you mentioned reputable manufacturers. Is there a good resource that you recommend for... If you're going to look at your own sunscreens that you've got in your closet and you want to kind of compare them to what's out there or find out if it's [01:14:00] good.

Brian Diffey: Well, I'm not going to recommend any manufacturers because I think that would be an [inaudible 01:14:04]. But I guess most of us know who the reputable pharmaceutical and cosmetic manufacturers are and-

Darya Rose: Just the big ones.

Brian Diffey: ... wherever you live. Yeah. I mean, you know, you, you do find some sunscreens on the market, you know, I'll wound up talking up in someone's garage, as it were. But, you know, there are in Europe, we have major manufacturers, like L'Oreal in France, Beyersdorf in Germany, Boots in the UK and so on. I mean, you know, I just think that three and, you know-

Darya Rose: Mm-hmm [affirmative].

Brian Diffey: ... you'll have, uh, you know, Johnson and Johnson in the US, you know?

Darya Rose: Got it. Yeah.

Brian Diffey: [inaudible 01:14:41]. You know, the companies that have got a good profile for the quality of that product.

Darya Rose: Okay. I personally really liked... We have an organization called the Environmental Working Group. Um, they have... I found their sunscreen guides to be very thorough and informative.

Brian Diffey: Sure. Yeah.

Darya Rose: And then I'll go ahead and link to that in the [01:15:00] show notes. Fantastic. Well, I don't have any other questions. It was wonderful to talk to you. I learned so much about sunscreen and how to apply it, and how to make good choices that I [laughs] feel. I hope everybody feels a lot of relief when they're making their choices.

Brian Diffey: Yeah, that's good. Okay.

Darya Rose: Wonderful. Thank you so much, Brian.

Brian Diffey: You're very welcome.

Darya Rose: Thank you so much for listening today. And I hope you learned as much from Dr. Brian Diffey as I did. As I mentioned earlier, this is the last show of season one, and I will be back in the fall to begin season two. In the meantime, it would help us a lot if you would leave us a five-star review over in iTunes and tell a friend about the show. We have a lot of fantastic shows planned for the next season, and I really look forward to seeing you then. Thank you. I'll miss you, and I'll see you next time.