Emily Wade (Host): We've had a very cold winter here in New England, but spring is right around the corner and before you know it, we'll be outside, soaking up that precious New England sunshine. That's why on this episode of Office Hours with MIT Health, we're tackling community questions about sun protection.

I'm your host, Emily Wade. And today, I'm welcoming our expert for all things skin-related, MIT Health dermatologist, Dr. David Li. Welcome to the show, David.

David Li, MD: Thank you so much for having me. I'm very happy to be here.

Host: Great. Before we jump in to our question, I just want to do a quick note. The info in this podcast is for general educational purposes only, and it's not a substitute for medical advice, diagnosis, or treatment. So David, I'm going to get right to our question from one of our community members.

Dear Office Hours, I'm a redhead and I get sunburns very easily. For that reason, I always buy the highest SPF sunscreen I can find. But SPF 100 costs a lot more than SPF 50. Do higher numbers really provide extra protection or at least enough extra protection to make them worth the much higher cost?

David Li, MD: Emily, that's a great question. And it's one that we oftentimes get asked in clinic. So, the short answer is, yes, the higher SPFs do offer more UV protection, right? To take a step back, SPF stands for sun protection factor. So as an example, we always see things that are SPF 15, SPF 30, SPF 50, and SPF 100.

So, SPF 15 blocks about 93% of UV rays. SPF 30 gets about 97%. And then, as you go up more, the curve really starts to flatten. So at SPF 50, you get about 98% protection. And then, you know, the jump from 50 to 100 only increases that by one more percentage point to about 99%.

Host: So if I'm hearing you right, it sounds like the difference between SPF 30 and SPF 100 is only about 2%. That's pretty small for such a big price jump.

David Li, MD: That's exactly right. So, you know, based on the math, a lot of people might ask like, why even bother? Like, why not just settle for like SPF 30 where you're kind of getting basically all you need in terms of the protection?

Host: But there has to be a catch, right? There's always a catch.

David Li, MD: A little bit, right? A little bit. I think there are instances where it is worth it shelling out for the additional SPF 50 or SPF 100 even at times, especially for those like our redheaded listener who essentially what we call is Fitzpatrick skin type I. Essentially, you go out into the sun, and then you don't tan at all. You just like immediately burn.

And I think the instance that makes it more reasonable to get something like the SPF 100 is having to do with human behavior, right? So, those SPF values are largely determined in like perfect lab settings, perfect conditions. And they're actually based off of applying about 2 milligrams of sunscreen per square centimeter of skin.

Host: So, how much is that in like real-world terms?

David Li, MD: That's about like one eighth of a cup or approximately a shot class full of sunscreen for the average person. But we know that in most cases we are definitely not applying that much onto our skin.

Host: So, this is like a lot of sunscreen. I definitely have a feeling most people are not putting this much on. On top of that, I'm assuming this is not the only mistake that gets made with sunscreen.

David Li, MD: Yeah, absolutely. I mean, there are a ton. I think most commonly we tell patiens that they typically need to reapply sunscreen every two hours. I mean, If you're not doing a whole lot, the every two hours thing might be a bit much. But let's say, you know, you're going swimming, or you're jumping into the pool, or you're sweating a lot, you may actually even need to reapply more frequently than every two hours, because the process of sweating the process of going into the water actually gets rid of a lot of the useful efficacious sunscreen that's currently on the skin. But as a rule of thumb, we tell people every two to three hours reapply the sunscreen. So, between applying too little and not applying often enough, I guess, the actual protection you're getting is far less than you might think.

Host: Okay. So, this is where the higher SPF is going to make the difference, I'm assuming.

David Li, MD: a hundred percent. Yeah. So, like our listener, that extra couple percentage points of UV protection might actually matter because it's more of like a safety net for them. I will say though, if applying SPF 100 makes you look very, you know, white cast and pasty and you're not going to wear the sunscreen, then I would much rather have the patient wear something that's like an SPF 30. So, the best sunscreen is going to be one that they're actually going to use on a day-to-day basis.

Host: That's a very good point. And now we at least know how much you should be putting on. Okay. So, that's a great answer for our redhead out there who I'm assuming they're maybe a Sloan listener since they wanted us to do some cost-benefit analysis there. David, would you be interested in any lightning round of our shorter questions that we've had come in?

David Li, MD: Sure. Let's do it.

Host: Okay. What ingredients should I look for in sunscreen? I want something that's effective, but that's also safe for me and the environment.

David Li, MD: That's a good question. So, I tend to think of it into two buckets, right? So, we have mineral sunscreens, and then we have chemical sunscreens. So, mineral sunscreens contain minerals like zinc oxide, titanium dioxide. So, essentially, they're like minerals that sit on top of the skin as you apply, and they work from the moment that you apply the sunscreen. So, you apply it, you go outside. It works just like that.

On the other hand, you have things like chemical sunscreens, which can contain a variety of different ingredients. And those actually take about 15 minutes or so to work, right? They have to get absorbed into the top layer of the skin. And then, they work by actually absorbing the UV and then converting it into heat that then kind of gets released from the surface of the skin.

So, the big difference here is that the first bucket of the mineral sunscreen does not get absorbed into your skin at all. The second, which is the chemical sunscreens, they've done some studies, I think in the last couple of years. There's one that was published in JAMA, which showed that if you actually apply enough of the chemical sunscreen onto your body, it has to be like a ton. You will find that there will be enough of the chemical sunscreens which go into the bloodstream, the serum, and it's measurable and detectable. What that means clinically in terms of safety is really we really don't know. So, I guess the other thing is that mineral sunscreens are generally safer for the marine life and reefs. I think that's what the question is getting at.

So, between those two, you know, I personally am fine with either mineral or chemical sunscreens based on the data. It doesn't show that one is necessarily more dangerous to you than the other. But I think if you're very environmentally conscious and you wanted to avoid things that could be bad for the reef and marine life, I'd probably go with a mineral sunscreen.

Host: That makes sense. All right. Here's another quick fire question. Spray versus lotion?

David Li, MD: I would definitely recommend a lotion. I think a spray is far less consistent. You're not sure how far to spray, you're not sure how much to spray, and then how much of it really is getting onto the skin versus being like blown into the wind. You know, like we're all used to that experience, like growing up by the beach or the pool. Like, we smell that kind of sunscreen spray being blown down wind. We're like, "Oh my God, what is that?"

Host: Yeah. It's like cloud of coconut smell.

David Li, MD: Exactly. Yep. Yep. So for that reason, I personally am much more a proponent for the lotion version, you know, where you're kind of getting a better sense of how much is actually going onto to your skin. There's less doubt about it.

Host: Okay. We've got one more lightning round question. I have darker skin and I don't burn easily. Do I still need sunscreen? And if so, can you recommend something that won't leave that white or ashy cast? So, I guess not the super high SPF, huh?

David Li, MD: Yeah. Short answer is yes. And I think this question is one that was, you know, previously, debated in the last, I would say, five, 10 years or so. It is like, do patiens with darker skin actually need sunscreen? So even though patiens with darker skin have more natural protection from essentially getting a sunburn, UV radiation is still happening. It still can cause sun damage, and it does increase the risks of certain types of skin cancers that are driven by UV.

In addition to this, patiens with more pigmented skin are actually more prone to things like hyperpigmentation or darkening of the skin, as well as conditions like melasma, which is that kind of, you know, hyperpigmentation around the face that we oftentimes see in some patiens, which is partly worsened by sunlight, but driven largely by other factors as well.

So, the question also was asking how do we avoid that kind of white cast. This is the perfect situation to talk about, I think tinted sunscreens. So, tinted sunscreens protect from the UV spectrum in addition to the visible spectrum. They do that by containing something called iron oxide, and it's very good. Tinted sunscreens are fantastic and I recommend them for patiens with light brown, kind of a little bit more pigmented skin where if you apply something that's a high SPF 50 or above, you'll look like you have that white cast. And the tinted sunscreens really help to prevent that from happening.

Host: That is really great advice. Even me, I've definitely looked like a mime before putting on that kind of like high SPF sunscreen. So, I think that's really helpful advice. All right. So, it sounds like we have learned that if you are going to use a lower SPF, you might want to think about using a higher amount of sunscreen. And we've learned a lot about different options of sunscreens that you can use and different applications.

Dr. Li, thanks so much for being here and clearing up the confusion around sunscreen today.

David Li, MD: Absolutely my pleasure. You know, I hope today's conversation is somewhat helpful for listeners, when they're thinking about how best to protect their skin, especially as we get into the spring, sunnier weather. I would like to say that, you know, whether you have a mole, you'd like to get checked out or struggling with acne, hair loss, skin growths or even warts, or you just want some expert advice on your skin. Our dermatology team is located at MIT Health and we're more than happy to help. You can make an appointment online and you don't need a referral.

Host: That is so awesome. That's good a reminder. I think I need to make an appointment myself. Thanks for a great episode of Office Hours with MIT Health. Thanks for tuning in. And if you have a question, stop by health.mit.edu/thrive and submit your question for one of our great clinicians to answer. Take care.