Scott Webb (Host): Welcome to BayCare HealthChat. I'm Scott Webb. Today we're going to do a little myth-busting with Dr. Dahlia Osment. She's a dermatologist with BayCare.

Doctor, it's nice to have you here today. We're going to do a little myth-busting. There's a lot of things that we all think we know about sunscreen, or we may have heard on social media or whatever, but we're going to rely on you and your expertise to bust some of these myths and give us some tips.

So let's start here. One of the biggest myths, if you will, that SPF 100 basically means I'm protected all day. Is that myth or fact?

Dr. Dahlia Osment: That's a myth, unfortunately. I wish it were true, but it's not true. So I think a good place to start would be to talk about what SPF actually measures. So SPF stands for sun protection factor, and it's important to know that it specifically measures protection against UVB rays. So UVB rays are the rays that are primarily responsible for sunburn and for skin cancer.

SPF doesn't tell us anything about UVA rays, which cause premature aging and wrinkles. So a common misconception is that SPF tells you how much time you can stay in the sun, but that's not actually how it works. A better way to think about SPF is in terms of how much UVB radiation it filters out. It's only measuring that UVB.

So SPF 15 blocks about 93% of UVB rays, SPF 30 blocks about 97%, SPF 50 blocks about 98%, and SPF 100 blocks about 99%. And that percent difference may sound small, but that extra 1 to 2% really can matter for people who are fair skinned, people who are on certain photosensitizing medications, or people who have a history of skin cancer.

Scott Webb: Yeah, because I was going to ask you, related to that higher number. So it does sound like the higher number gives us more protection, but by no means does SPF 100 just mean we're covered, right, for the rest of the day?

Dr. Dahlia Osment: Yes. So in terms of higher SPF being better than lower SPF, it is, but only up to a certain point. For most people, I recommend at least SPF 30 daily and SPF 50 when spending extended times outside on the boat or at the beach. The biggest mistake people make isn't choosing an SPF 30 instead of an SPF 50. The biggest mistake people make is really not applying enough of it or not reapplying it.

Scott Webb: Yeah, I wanted to ask you about that because I've heard that before, about the importance of reapplying, right? Especially with my kids. When I would put sunscreen on them when they were little, in the morning they figured they were covered, and they definitely didn't want dad to do it again. So let's talk about the importance of reapplying.

Dr. Dahlia Osment: Sure. So it's really important because sunscreen doesn't stay where we put it. So it gets broken down by sunlight, rubbed off by clothing, wiped away by towels, diluted by sweat and by water. So even if you do a perfect job applying it in the morning, your protection decreases throughout the day.

I recommend reapplying every two hours when you're outside. And it's really important to know that you should be dry when you're reapplying it. So if you're getting out of the water or if you've sweat, you want to wipe yourself down so you're dry, and then apply it.

Scott Webb: Right. All right, I've got another myth for you here, Doctor. If it's cloudy and cooler out, or I'm mostly in the shade, I can probably just skip sunscreen.

Dr. Dahlia Osment: Yeah. Unfortunately, also not true. So up to about 80% of UV rays penetrate clouds which means you can absolutely get significant UV exposure on an overcast day. In fact, a lot of people are surprised by how badly they burn when it's cloudy because they don't feel the heat of the sun. And it's important to realize that temperature is totally unrelated to UV radiation.

It can occur on a cool winter day just as it can on a hot summer day. And the shade helps, but it doesn't completely protect you. UVA rays reflect off of surfaces, like water, sand, concrete, snow, and even nearby buildings. And it's also important to know that UVA rays penetrate window glass. So when you're driving in the car or when you're sitting by a window, UVA rays do penetrate through that glass.

Scott Webb: Of course. Another myth, Doctor, and I know maybe it's fueled by the sunscreen industry, that waterproof or sweatproof sunscreen is really a thing. Are they a thing?

Dr. Dahlia Osment: So, they used to be. The FDA actually doesn't allow sunscreen manufacturers to use the term “waterproof” or “sweatproof,” because no sunscreen is truly waterproof. So now instead, you'll see “water resistant” on the label. And that means the sunscreen maintains its stated SPF for either 40 or 80 minutes while swimming or sweating.

So it'll say on the product, “water resistant for 80 minutes” or “water resistant for 40 minutes.” But you still, of course, need to reapply.

Scott Webb: Yeah, we really should reapply, especially if we are going in the water or we're sweating, right?

Dr. Dahlia Osment: Yes, correct.

Scott Webb: Another myth for you here. I need sun exposure or a tan for vitamin D, so sunscreen is bad.

Dr. Dahlia Osment: Yeah. So this is one of the ones we hear most frequently from patients.

Scott Webb: I’m sure, right?

Dr. Dahlia Osment: And this is a myth that's unfortunately persisted for years. So while sunlight can absolutely help your body produce vitamin D, intentionally tanning isn't a safe option or way to get it. A tan is actually evidence of DNA damage occurring in the skin.

So the good news is that vitamin D can be obtained through diet and supplements without increasing your risk of skin cancer or premature aging. So foods like fatty fish, fortified dairy, fortified cereals, those contain high amounts of vitamin D. And then for people who need additional supplementation, supplements are relatively inexpensive, safe, and very effective.

So as dermatologists, we would much rather see someone take vitamin D supplements than accumulate years of preventable UV damage.

Scott Webb: So just to finish up here, Doctor, some tips from an expert, if you will. What should we look for on the sunscreen label? Because I know just in my experience, anecdotal at best here. But when I stand there in the aisle at the store and I start reading the packaging for sunscreen, my head just starts to spin, and I don't know what to do. So from you.

Dr. Dahlia Osment: It can be overwhelming. So, first thing you want to do is turn the bottle over. You want to look at the back of the bottle, and you want to look at the active ingredients. There are two major types of sunscreens. There are chemical sunscreens and there are mineral sunscreens. So mineral sunscreens are, in my opinion, and the evidence supports it, superior in terms of their coverage and their protection to the chemical sunscreens.

So a mineral sunscreen is going to have zinc oxide and/or titanium dioxide as the active ingredient. A chemical sunscreen is going to have those longer words, so octinoxate, oxybenzone, benzophenone. Those are chemical sunscreens. And while they still work and they're better than no sunscreen, the mineral sunscreens are superior in protection.

So you want to turn that bottle over, look for the word mineral sunscreen or zinc oxide or titanium dioxide. Once you've met that criteria, this is when you want to look at the number. So 30 or higher is really what we should aim for. And then you're also going to see a stamp on the front of the bottle that says broad spectrum protection. So broad spectrum protection with a mineral sunscreen that's SPF 30 or higher.

But I like to say the best sunscreen is the one that you'll actually reach for. So whether it's a cream, lotion, stick, a gel, spray, they can all work if they're rubbed in and applied correctly and reapplied.

Scott Webb: Right. I never really know how much sunscreen is enough sunscreen, right? Should I be able to see my skin at all through the sunscreen?

Dr. Dahlia Osment: Yeah, so this is important. I'm glad you brought this up. So this is where most people fall short. So for the face alone, adults need what we call the two finger rule. So, if you stick out your index and your middle finger and take sunscreen and draw out two full strips of sunscreen squeezed along the length of your index and middle finger, that's just what you need for your face every two hours.

So a lot of times people don't rub in the product well. This is where cosmetic elegance comes into play because there's a lot of mineral sunscreens on the market, and some are more cosmetically elegant than others. So it's good to try a few until you find one you like, but it should rub in. So two finger lengths for your face. And then for the entire body, you need about the amount that fits in a shot glass, so about one ounce to cover your whole body, and that's every two hours.

And most people only use about a quarter to a half of the amount tested in the lab, which means they're getting significantly less protection than what's listed on the bottle if not applying enough. So most sunscreen failures aren't sunscreen failures, they're application failures.

Scott Webb: That's well said by an expert. I feel like that could fit on a t-shirt somewhere.

Dr. Dahlia Osment: I have one.

Scott Webb: Yeah, I'm sure. And we've all been there, of course, Doctor. Like, we do our best. We try, but you always end up missing a spot, and that's always the spot the sun finds, right? It has a knack for doing that.

Dr. Dahlia Osment: Right.

Scott Webb: Well, listen, I really appreciate your time and your expertise today. These are universal topics. We all face this, and whether it's in the summer or the winter, if we're exposed as you're saying here, the sunscreen we'll use is the right one, the one that we'll reapply is the right one, and we'll all just keep fighting the good fight as I know you will. So thank you so much.

Dr. Dahlia Osment: Yes, my pleasure. Thank you.

Host: And that wraps up this episode of BayCare HealthChat. Head on over to our website at BayCare.org for more information and to get connected with one of our providers. Always remember to subscribe, rate and review this podcast and all of the other BayCare podcasts, so we can share the wealth of information from our experts together. I'm Scott Webb. Stay well.