The Science of Sunscreen

by Emily Caporello

All your life you’ve been told to wear sunscreen. Your mom told you to, your pale freckly friend told you to, it was in that stupid song that radios played all the time when you your much older sister graduated high school, but you just whined whyyy and sprayed yourself with a verboten bottle of Hawaiian Tropic tanning oil when no one was looking (SPF 5 is still SPF, amiright!). But now that you’re old and afraid of wrinkles (and cancer, of course, but… mostly wrinkles) here’s a little info to help you understand just what on earth sunscreen even is and why we need it.

In case you spent physics class daydreaming about what Mr. Tupii’s biceps looked like under his long-sleeve button down (he had just graduated college, OK! Seriously he was like 23, it wasn’t creepy), I’m going to blow your mind and inform you that light particles (photons) are really waves, and the sun spits these waves out in a range of sizes, just like these waves. If they’re within a tiny range of sizes (say, between a body wave and a deep wave), we can see them because our eyes have special cells that detect those size waves and turn them into brain signals. If the light waves are just a bit smaller than the smallest light waves we can see (a “jeri” size wave, in this analogy) then they are called ultraviolet. Ultraviolet light sounds pretty, but like many pretty things it is actually evil: It will burn your skin and give you wrinkles. Smaller light waves like UV are powerful enough to kick electrons out of their tiny homes where they live in your skin molecules, damaging your skin and creating the crazy, destructive monsters that are free radicals. The smaller the wavelength, the more damaging the light is to your skin.

Luckily, the ozone layer protects us by preventing most UV light from getting to us. Unluckily, the ozone layer is still pretty pissed at us for trying to kill it with CFCs, so it lets just enough through to give us sunburns and cancer. Most of the ultraviolet light that gets through is UVA, which has the biggest wavelengths of all UV light and is the least damaging. But much like my ex-boyfriend’s mouth, the ozone occasionally lets through something nastier than the typical, mildly irritating bs. UVB, a type of ultraviolet with a smaller wavelength than UVA, is powerful enough to jolt around electrons in your DNA and cause them to form new chemical bonds, changing their structure. This creates a genetic mutation. And if I know anything, it’s that genetic mutations cause super powers cancer. UVB produces such a reliable mutation that it is called a “UV-signature” mutation, and it can directly lead to basal cell and squamus cell carcinomas.

In order to fight ultraviolet light on its own, skin has this sort of magical defense called melanin. When your skin is initially damaged by UV radiation, it sends out an SOS to melanin-containing cells. Bravely, melanin comes to the rescue, standing between the sun and the DNA of your skin cells, absorbing UV light and, most importantly, giving you a sun tan (!!!). Just to be clear, the tan occurs because YOUR SKIN IS DAMAGED. There is NO WAY to get a natural tan without damaging your skin. It’s science. Sorry. And once all the available melanin is used up, the damage worsens and your skin becomes inflamed and red and, yes, sunburned.

Because sunburns are such a huge pain in the neck (bam!), a chemist in the 1930s had this bright idea to make the first topically applied sunscreen. It was awesome and everyone loved him. The end. Two issues though — first, even though traditional chemical sunscreens block UVB light (preventing sunburns and direct DNA damage), UVA light is still free to do its thing. UVA won’t directly eff up your DNA or damage your cells enough to cause a sunburn, but it can go deep into your skin to create free radicals and damage proteins like collagen. This means wrinkles. It also means indirect DNA damage and the deadliest cancer of all the skin cancers — malignant melinomas. And now that people can go out in the sun without getting burned, they are staying out in the sun longer = more UVA exposure = increased risk of lethal skin cancer = bad. Second, just when you thought you were (finally) becoming that girl that does morning yoga and eats vegetables and doesn’t make out with people’s boyfriends and is generally a healthy human being, scientists discovered that once the sunscreen you so piously applied is absorbed into the skin, UV light can alter the sunscreen chemicals (specifically octylmethoxycinnamate, benzophenone-3, and octocrylene) to create free radicals, potentially giving you lethal skin cancer as well. Umm, wtf. You might as well have been smoking this whole time.

To fix the first issue, Boots in UK created a fancy new star system to tell you how much UVA protection your sunscreen has. You can’t tell UVA protection from the sunscreen’s SPF rating, because that only measures how good a sunscreen is at preventing a sunburn (i.e., blocking UVB light). Use this amazing infographic to help you determine how much UVA and UVB protection you need depending on your skin type, the weather and elevation, etc.

In regards to the second issue, that sunscreens may actually cause free radical damage rather than prevent it, there are several (somewhat unsatisfying) options to choose from.

– The first is to stick to physical sunblocks, like zinc oxide or titanium dioxide, which reflect UV light rather than absorbing it. All sunscreens have the potential to create free radicals upon UV exposure, but these oxides are generally considered among the safest options. You may remember zinc oxide from such public appearances as with spicoli and ug. For those of us less willing (or able) to revive the questionably sexy white-sunscreen-nose trend, there are now clear sunblocks available made with very very tiny zinc oxide and titanium dioxide particles which, well, may or may not be safe.

– You could also try some of the newer, more “photostable” chemical sunscreens (such as Mexoryl or Tinosorb), which were developed to stay structurally intact over longer periods of UV exposure. Because these chemicals are new, however, there is limited data on their safety.

– You could also keep using your dangerous free-radical-causing sunscreens alongside an effective antioxidant since, as we covered previously, the antioxidants should help neutralize free radicals. Additionally, reapply your sunscreen frequently so that once the old sunscreen is absorbed into the skin, a new layer is sitting on top of the skin preventing UV light from getting through. This should theoretically prevent the absorbed sunscreen from reacting with UV light and causing damage.

Whatever sunscreen you choose, I highly suggest heading over to the outstanding environmental working group beauty database to see how likely on a scale of 1–10 your sunscreen is to hurt you (then spend five hours checking every other skin and hair product you own). The SPF 30 coppertone sport I’ve been using for months is a 7! Someone pass me the chemo sign-up list! AHAH! AHAHAhaha!…

Finally, you could pick the last option, which all of you will roll your eyes at and reject as quickly as you did in sex ed: abstinence. Wear head-to-toe clothing or better yet, never go outside at all! Seriously guys, if you need me I’ll be in my basement re-watching Game of Thrones and slathering myself in Retin-A until it’s daylight savings time. We can bond over our pale, wrinkle-free, vitamin D deficient skin then.

(Learn even more!)

Previously: A Lady’s Guide to Anti-Aging Cream.

Emily Caporello is a very vain scientist in San Diego.