PODCAST Sun Protection with Dr Jonette Keri

 

 

Host: Welcome to another episode of the MSD Manual's Medical Myths Podcast. On this show, we set the record straight on today's most talked about medical topics and questions. Protecting your skin from the sun is one of the most effective ways to reduce the risk of skin cancer, premature aging, and sunburn. Today, we're discussing sunscreen, and I'm sure we've all heard plenty of confusing information about how it works, when it works, and what's the best type of sunscreen to use. I'm your host, Jason Rocker, and to help answer those questions is Dr. Jonette Keri. Dr. Keri is a professor of dermatology and cutaneous surgery at the University of Miami Miller School of Medicine and the chief dermatology service at the Miami VA Hospital. Thanks for joining us, Dr. Keri.

Dr. Keri: Thank you, Jason. I'm happy to be here.

Host: So obviously we're talking about sunscreen, sun protection. We hear sunscreen and sunblock kind of used interchangeably all the time. Is there actually a difference and is sunblock still the right term that we should be using?

Dr. Keri: I don't think it really matters in the sense that people should pick something that protects their skin, but we like sunscreen. Think of a block as being something permanent and a screen as being something that a little bit of something might get through. So sunscreen is what I would call.

Host: So one of the biggest questions people have about sunscreen is, is it better to use chemical versus mineral sunscreen? What's the difference between the two and how does each one work to protect our skin from the sun?

Dr. Keri: So think of it this way, it's pretty simple. A mineral sunscreen is something that is on top of the skin and the sun comes and is scattered off of it. It is basically a blocker, we just talked about blocking, but it basically provides a layer and then the sun is scattered off of it. The difference between that and a chemical sunscreen is that a chemical sunscreen requires a chemical reaction and it stays, think of it as having a reaction and staying there on the skin. When the sun comes down, that chemical reaction occurs and it stays there on the skin.

Host: Now, do you think most people who are buying sunblock really know the difference between a. You have to read the label pretty intensely to have an understanding whether it's mineral or chemical, and then what's more common?

Dr. Keri: So you'll see a lot of both. And what is probably more common is something that gets both UVA and UVB. We're going to talk about this in a little bit because you want to get that entire spectrum of the UV light. The ones that we have approved in the United States that are chemical, none of them get completely UVA and UVB, and that's why you'll see those chemical sunscreens often paired together different formulations of them. The mineral sunscreens do get all of UVA and UVB, so that's why sometimes people will pick a mineral sunscreen and that's why you'll see them often as the active ingredient by themselves.

Host: Is one type better for a certain type of skin or for certain type of activity? Should you choose a mineral sunscreen over a chemical sunscreen or vice versa?

Dr. Keri: So we think that the best one is the one that you're going to use, but in general for sensitive skin, we go more towards the mineral sunscreens.

Host: And in terms of sensitive skin versus different skin pigmentations, tones, et cetera, is there a different one that some people should use or does that affect the kinds of sunscreens that people are using?

Dr. Keri: Well, people with skin of color, darker skin of color, they may want something that helps prevent hyperpigmentation. And one part of a sunscreen component that isn't listed as an active ingredient is iron oxide. So iron oxide will be listed down below and that can actually help with the pigmentation issue. But as far as which one they choose for darker skin types, oftentimes people with darker skin don't want to look whitish from the zinc or titanium mineral sunscreens. So they may want a chemical sunscreen, but if they're looking for pigmentation help or hyperpigmentation help, they should use something that has iron oxide in as well.

Host: Got it. And what about different kinds of activities? One, I guess if you're just kind of hanging out in the beach versus two, if maybe you're out playing softball or some other activity where you're sort of active and moving, is there a difference in terms of what type of sunscreen we should be using in those different situations?

Dr. Keri: So know that water resistance is not waterproof. A lot of times people will say, "I want a waterproof sunscreen." There is no waterproof. It's water resistant from 40 to 80 minutes is the most we have on our sunscreens in the United States. So that's one thing. So if you want to be in the water, you might want something that says water resistant. If you're worried about something that is maybe going to get in your eyes and burn when you're sweating, maybe you want something that's more for, let's say a baby, because usually a lot of those formulations aren't as burny if they get in the eyes.

Host: And in terms of, we talked a little bit about skin pigmentation, does that change how frequently someone should be applying sunscreen if you have a lighter pigmentation versus a darker pigmentation or sort of the spectrum along the way?

Dr. Keri: So if you are fair skin and you're in an area with a lot of sun as we are in Miami, you're probably going to be putting on sunscreen almost every day of the year. Maybe a few days in January you don't need it. If you're a darker skin type and you're not out in the sun much, you really don't need sunscreen. And we have to remember, and the Australians did a really good job of this back in 2024, what the Australians did is they broke down who should use sunscreen when by skin type. If you were a darker skin person and the UV index, which is sort of a way that we look at how bright the sun is that day, is below three and you're not going to be out the sun for a lot of time, you don't really need a sunscreen, especially if you're darker skin.

But if you are, let's say a person who has lighter skin and you had a skin cancer, then you might be putting on that sunscreen even with a low UV index. So with respect to do darker skin types need sunscreen, not all the time, and we want to make sure those populations get enough vitamin D.

Host: I've heard whether it's a myth or not, I don't know, but that people should put on a lotion every day that has some type of sunscreen in it. Is that best practice? Is that overkill?

Dr. Keri: It all depends where you live. So in preparation for us speaking today, what I did is I looked at the UV index around the country and the UV index in Florida was like a 12 when I looked in Miami. And up in Vermont where my good friend from medical school lives, it was between a one and a two. So ideally in a place like that, she doesn't need to put on sunscreen with a low UV index. She hasn't had a skin cancer. She is lighter skin. But for that example, it depends on where you live and your skin type. I don't think everybody needs a sunscreen on every day. I think it all depends on where you live and what your goals are. If you are an athlete that's out in the sun all the time, even if you're darker skin type, you may not want that hyperpigmentation. So what your goals are, what you're trying to prevent and where you live.

Host: Is there a downside to it? Let's just say for sake of argument, hey, you get in the habit every day, you put a lotion on because you want to make sure your skin's moisturized and it happens to have a SPF in there. Is that fine to do?

Dr. Keri: That's fine to do, but I usually tell people if you're putting on a sunscreen with lotion every day, I think it's better to take a shower at night and put on the lotion that's not for the day at night.

Host: Got it. And in terms of if, let's just say for sake of argument, you're at the beach for the day, how often should someone be applying a sunscreen? Is there a rule of thumb that says it's every three hours or is it different for different SPFs or just be interested to know that?

Dr. Keri: So generally we say about every two hours, but really sometimes you need it every hour. If you're feeling like your skin is burning or you're feeling it's too hot. So generally we say about every two hours, but remember that water resistance we talked about, it's only 80 minutes and that's an hour and 20 minutes. So if you're in and out of the water, you're probably going to want to do it more frequently than every two hours.

Host: Got it. Is there a best way to sort of apply the sunscreen? And you know it comes in different, whether it's a lotion or an aerosol spray. Do you have a preference?

Dr. Keri: So spray should be done outside. Spray should be done outside. And as far as sunscreen, I always say to make sure you put enough on and what is enough. It's about a shot glass for your whole body and about the size of a quarter for your face and your neck so you have an idea how much you're putting on what you put on. Most people do not put enough sunscreen on.

Host: If you have a spray, are you less likely to cover an area fully as opposed to a lotion where you actually are rubbing it in and can see it as opposed to spraying it around or what's your experience there?

Dr. Keri: No, to be honest, I think the spray is as long as there's a thin layer of wetness and then you can sort of rub it around when you get that spray on. I think you're fine with the spray. I think the important thing is finding the formulation that works for you and your family or your friends or whoever. I find that sticks are very good for some people who don't like to put on lotions. There are a lot of stick formulations. So there are a lot of different formulations out there, but see what works best for you.

Host: Great. And I know sometimes when it's cloudy out, people have a tendency to get a little complacent. Is cloud cover a protectant from the sun or do we need to be extra aware when it is cloudy because we get a little bit careless?

Dr. Keri: Same thing we talked about before. Look at that UV index. They have them all over the place. My young resident today, I talked to her about the UV index. She had it on her watch on her phone, so her phone watch, these things. So she was like, "Oh, the UV index today is." So you still get a fair amount of UV through the clouds. Back in the day, they used to say up to 80%. I can't say that that's the same all the time because the clouds are different, but I would use the UV index. So you are not safe on a cloudy day, and many of us with fair skin have gotten burned on cloudy days.

Host: Got it. We talked a little bit about SPF. We kind of alluded to it earlier. Can you just give us a little bit of an insight into what SPF stands for, what does it actually measure, and is there a particular SPF level that you recommend for most people?

Dr. Keri: So SPF is sun protection factor, and it is only the protection against UVB. So when you see SPF 30, you are not getting protected against UVA. Now let's talk about UVB and UVA a little bit. UVB, that is the sun's rays, or those are the sun rays, I should say, that burn your skin. And they can cause cancer and they can cause burns and they can cause all those things. But UVA are the deeper rays, and those can also be bad for you. And that's why on sunscreens, you'll see SPF 30 and then you'll see broad spectrum. Broad spectrum gets the UVA part. SPF 30 only gets the UVB part. So you really need an SPF of at least 30 in answer to your question that also says broad spectrum.

Host: Got it. So most people really just know SPF, right? Right. So we need to educate people and let them know what that broad spectrum is. So let's hit that again so our listeners get a good understanding of it.

Dr. Keri: Sure, sure. So SPF is the number that protects you against the UVB rays. There's UVA and UVB. We have to protect against both of them. So SPF 30 means you can stay on the sun about 30 times longer than you normally would without burning. The thing about SPFs, and everybody gets caught up, I'm on a 30, but you need that second part of the sunscreen label where it says broad spectrum and that gets UVA. So you want an SPF 30 and broad spectrum. As I alluded to earlier, all of the chemical sunscreens that we have approved in the United States, none of them get all of UVA and UVB. That's why you see them combined together with different things or they might be combined with a mineral sunscreen. The mineral sunscreens do get all UVA and UVB with zinc being a pinch better than titanium.

Host: I guess that's my question is 30, if that's the minimum, why not do 50? Why not do 70? What's the difference? So you can stay out 30 is 30 times longer, 50 is 50 times longer, 70 is 70 times longer.

Dr. Keri: The main reason that people pick a higher one is most people don't put on enough sunscreen. So if they put on a 30 and they put on a thin layer, they're probably getting a 15 or maybe a 10. So if you're getting a 50 and you're putting it on, you're probably getting a 25 if you're not putting enough on. So generally people don't put on enough sunscreen.

Host: So it's the user error that gets you, right?

Dr. Keri: Sometimes, yes, for sure. Sometimes.

Host: Talk to us a little bit about the ingredients in sunscreen, right? We know there's a lot of different ingredients. We see a lot of different stuff. Can you talk to us about the safety of different ingredients and maybe what people see on social media versus what's real in real life?

Dr. Keri: Sure. So most of the social media bad boys have been in the chemical sunscreens, and that's because in vitro studies, which are test tube, think of it as a test tube or a Petri dish, and in animals, there have been some bad effects with respect to neurology and reproduction, but none of those have been repeated in humans, and there is no evidence to suggest that those chemicals will cause problems in humans because these studies need to have very high doses. That's not done. They're not reproducible. So I want you to understand that those products are safe. However, people get worried because you'll see that some of these sunscreens are banned in certain areas, and that goes with respect to also environmental concerns. So there are some concerns. For example, we're in Miami and we're pretty close to Key West. And in Key West, for example, they have banned some of the chemical sunscreens because of the coral reefs and there's concern about the coral reefs.

So it's sort of a twofold. People are worried about the chemical sunscreens with respect to cancer, reproduction, neurologic problems, but then they're also worried about the coral reefs. Now, the coral reef data is very interesting and it's very sort of difficult in a way because of the fact that global warming is already occurring and the heat of the water probably with the sunscreen, I'm just saying probably because I'm not a marine biologist, the two together are hurting our coral reefs, not just the sunscreen, but probably the warming of the water. And then you throw the sunscreen on top of it that may cause some problems. So that's why it's these types of products, I should say. That's why these types of products are banned in certain areas, including in our neighbors in Key West. Understood. Is there a particular ingredient that people should be looking out for that is readily available in sunscreen?

People get worked up about oxybenzyl. So oxybenzone, that's one of the ones that some of the original studies showed some concerns with reproduction and embryos and all types of things, and none of them that has been confirmed in anything in humans. The trouble with oxybenzone is that it's almost ubiquitous in personal care products or some form of it. So what does that mean? So it's pretty much everywhere. Oxybenzone is a wonderful sun protection agent when combined with something else. Remember, it doesn't get them all oxybenzone. You're going to see it with some other things.

Host: Understood. So the reality is people are getting that in many other different aspects of their life, and if it helps protect you from the sun, maybe it's not something you need to worry about so much.

Dr. Keri: Right. You don't need to worry about as much. Now, I do want to not call out the zinc and titanium because a lot of people worry about zinc and titanium, and although those sunscreens get every spectrum of the UV that we're concerned about, there has been some hype about nanoparticles, which are very small particles, and they do that so you don't see the whiteness when you put on the zinc or titanium. So they make them very small to the minus nine nano. And there was some hype that you could see this also in your urine afterwards, but it was thought to be safe. And I'm going to tell you personally, I will rather have the white and I'll go for a micro, a minus six in my sunscreen. So we all get a little cautious about things. I don't need to have the clear zinc. I will sometimes use the minus six, but again, no data to show that the nano is bad. They call it nanoparticle.

Host: What are some other ways that people can protect themselves from the sun? What should we be recommending if they're going to be out in the sun? What are some other potential things that they can do?

Dr. Keri: So hats are huge. And as I've gotten older, I wear hats. When I was young, I didn't want to wear a hat. Oh my goodness, hats make such a difference. Hats, clothing, seek the shade. Wherever you are, know that I walk across campus. We have three hospitals here. I walk between them. I go to the shady side of the street. Also, I want people to know that the light can reflect off of surfaces, not just boats and water and shiny things like glass. It can reflect off of concrete. So even if you're wearing that hat on, you might want to have your sunscreen and your hat, it's reflecting off if you're in a city environment with a lot of sun. And I would also caution people to protect some other areas that we forget about. And one of the things that I say when we talk about protecting is I would encourage people to protect their eyes with sunglasses and to protect their lips because people put the sunscreen here, but then they don't put it on their lips. And eyes, sun exposure on the eyes can lead to cataracts and to macular degeneration. So I would tell you to protect your eyes and your lips as well when you're going out because we might forget those.

Host: Great. No, those are great tips. Now obviously we're on a myth busting podcast here, so let's bust some myths. What are some of the biggest misconceptions you hear about sunscreen or sun protection in general?

Dr. Keri: So one of the biggest myths is that sunscreens cause cancer. They don't. There's no proven evidence that sunscreens cause cancer. So I would please ask people to not perpetuate that myth, that you only need sunscreen when you go to the beach or in the summertime. Again, you want to look at your skin type. You want to look at the environment in which you live. I wear sunscreen every day, that good old UV index of three, which is sort of a cutting point. We hit that a few times in the last year in Miami. So I should have had sunscreen on almost every day. Some other myths about the sun or about sunscreen, I guess, are that you can get enough in your moisturizer. We sort of alluded to that before, but if you put on just a moisturizer with an SPF 15, you're probably not going to get enough. And you want to make sure you get that broad spectrum too.

Host: Got it. Okay, that's great. Now, I remember when I was growing up way back in dad, I had an older sister and she would put baby oil on when she went into the sun, and sometimes they'd even put iodine in there, if I recall correctly. I hope no one's doing that anymore, right? There's really some dangers to that, isn't there?

Dr. Keri: Yeah. It just magnifies the sun's rays, right? And many people did that. I did that as a teenager, a little bit of baby oil. I think almost everybody did in my generation, but that magnifies the sun's rays. So we want to try to avoid that.

Host: That's great. And if there's one thing that everyone misunderstood about protecting their skin from the sun, what would it be?

Dr. Keri:  It's that every ray of sun you get is cumulative and people forget this. It's like a bank account. It adds up, but not always in the best way. You need some sun. We need sun. The sun is good. It gives us some vitamin D, makes us feel good, but remember that every ray you get is cumulative. So I have a lot of young people say that they'll worry about that when they get older, but the fact of the matter is that same young person, now I'm taking care of sometimes three generations of families where I've seen them for that many years and they start wanting to use sunscreen to protect themselves from aging at 40. Well, some of that aging was going on back when you were a little guy running around at the beach. So please know that sun exposure is cumulative, not just for cancer, because most people aren't going to get skin cancer, but everybody's going to age. But to prevent aging to move as quickly as it goes, they should watch the sun.

Host:  Got it. Thanks. Dr. Keri, thanks so much for joining us on the MSD Manual's Medical Myths Podcast. As we close out, I'll let you leave our listeners with one final word.

Dr. Keri:  Medical knowledge is power. Pass it on.