Not so long ago, people like my Aunt Muriel thought of sunburn as a necessary evil on the way to a "good base tan." She used to slather on the baby oil while using a large reflector to bake away. Aunt Muriel's mantra when the inevitable burn and peel appeared: Beauty has its price.
Was she ever right about that price — but it was a lot higher than any of us at the time recognized. What sun addicts didn't know then was that we were setting our skin up for damage to its structural proteins and DNA. Hello, wrinkles, liver spots and cancers. No matter where your complexion falls on the Fitzpatrick Skin Type scale, ultraviolet radiation from the sun or tanning beds will damage your skin.
Today, recognition of the risks posed by UV rays has motivated scientists, myself included, to study what's going on in our cells when they're in the sun — and to devise modern ways to ward off that damage.
When sun hits skin
Sunlight is composed of packets of energy called photons. The visible colors we can see by eye are relatively harmless to our skin; it's the sun's ultraviolet light photons that can cause skin damage. UV light can be broken down into three categories: UVA, UVB, and UVC. UVA and UVB each reach earth and our skin, but UVC is blocked by the ozone layer above earth throughout most of the world.
Our skin contains molecules that are perfectly structured to absorb the energy of UVA and UVB photons. This puts the molecule into an energetically excited state. And as the saying goes, what goes up must come down. In order to release their acquired energy, these molecules undergo chemical reactions — and in the skin, that means there are biological consequences.
Interestingly, some of these effects used to be considered helpful adaptations, though dermatologists today consider them indications of damage. For example, tanning is due to the production of extra melanin pigment induced by UVA rays, and both UVA and UVB also turn on the skin's natural antioxidant network.
That extra melanin blocks some UV light from reaching our DNA, but plenty still gets absorbed. When DNA releases that energy, it can cause mutations, which means skin cancer: both non-melanoma (basal cell carcinoma, squamous cell carcinoma) and melanoma.
Our UV-activated natural antioxidant network is not foolproof, either. Antioxidants have a big job: destroy free radicals and reactive oxygen species (ROS) before they can mess with pretty much anything that gets in their paths. ROS are a natural byproduct when some skin molecules absorb UV light — left unchecked they can cause DNA mutations and skin wrinkles. When our antioxidant network is overloaded, then "oxidative stress" has set in, and damage to our skin cells is the result.
We know that UVA light penetrates deeper into the skin than UVB, destroying a structural protein called collagen. As collagen degrades, our skin loses its elasticity and smoothness, leading to wrinkles. UVA is responsible for many of the visible signs of aging, while UVB light is considered the primary source of sunburn. Think "A" for aging and "B" for burning.
The end result of all of these photoreactions is photodamage that accumulates over the course of a lifetime from repeated exposure. And — this cannot be emphasized enough — this applies to all skin types, from Type I (think Nicole Kidman) to Type VI (think Jennifer Hudson). Regardless of how much melanin we have in our skin, we can develop UV-induced skin cancers, and we will all eventually see the signs of photo-induced aging in the mirror.
Before the damage is done
The good news, of course, is that the risk of skin cancer and the visible signs of aging can be minimized by preventing overexposure to UV radiation. When you can't avoid the sun altogether, today's sunscreens have got your back (and all the rest of your skin, too).
Sunscreens employ UV filters: molecules specifically designed to help reduce the amount of UV rays that reach through the skin surface. A film of these molecules forms a protective barrier, either absorbing (with chemical filters) or reflecting (with physical blockers) UV photons before they can be absorbed by our DNA and other reactive molecules deeper in the skin.
The Food and Drug Administration regulates sunscreens as drugs. Because we were historically most concerned with protecting against sunburn, 14 molecules that block sunburn-inducing UVB rays are approved for use. That we have just two UVA-blocking molecules available in the United States — avobenzone, a chemical filter; and zinc oxide, a physical blocker — is a testament to our more recent understanding that UVA causes trouble, not just tans.
The FDA also has enacted strict labeling requirements, most obviously about SPF (sun protection factor). On labels since 1971, SPF represents the relative time it takes for an individual to get sunburned by UVB radiation. For example, if it takes 10 minutes typically to burn, then, if used correctly, an SPF 30 sunscreen should provide 30 times that: 300 minutes of protection before sunburn.
"Used correctly" is the key phrase. Research shows that it takes about one ounce, or basically a shot-glass-size amount of sunscreen, to cover the exposed areas of the average adult body, and a nickel-size amount for the face and neck (more or less, depending on your body size). The majority of people apply between a quarter to a half of the recommended amounts, placing their skin at risk for sunburn and photodamage.
In addition, sunscreen efficacy decreases in the water or with sweating. To help consumers, the FDA now requires sunscreens labeled "water-resistant" or "very water-resistant" to last up to 40 minutes or 80 minutes, respectively, in the water, and the American Academy of Dermatology and other medical professional groups recommend reapplication immediately after any water sports. The rule of thumb is to reapply about every two hours and certainly after water sports or sweating.
To get high SPF values, multiple UVB UV filters are combined into a formulation based upon safety standards set by the FDA. However, the SPF doesn't account for UVA protection. For a sunscreen to make a claim as having UVA and UVB protection and be labeled "broad spectrum," it must pass the FDA's Broad Spectrum Test, where the sunscreen is hit with a large dose of UVB and UVA light before its effectiveness is tested.
The broad spectrum test was established in the FDA's 2012 sunscreen labeling rules and acknowledges something significant about UV filters: Some can be photolabile, meaning they can degrade in UV light. The most famous example may be PABA. This UVB-absorbing molecule is rarely used in sunscreens today because once it does its intended job and absorbs UV light, it degrades into other chemical forms that elicit an allergic reaction in some people.
The only chemical UVA filter on the market, avobenzone, is also photolabile. It degrades when it absorbs UVA light, leading to a loss in its ability to protect our skin from UVA. But there are ways to make avobenzone more stable. Savvy consumers should look for octocrylene in the "active ingredient" list of their sunscreen or ethylhexyl methoxycrylene as an "other ingredient." Both can help keep avobenzone from degrading as quickly between reapplications.
Antioxidants
Next up in sunscreen innovation is the broadening of their mission. Because even the highest SPF sunscreens don't block 100 percent of UV rays, the addition of antioxidants can supply a second line of protection when the skin's natural antioxidant defenses are overloaded. Some antioxidant ingredients my colleagues and I have worked with include tocopherol acetate (vitamin E), sodium ascorbyl phosphate (vitamin C) and DESM. And sunscreen researchers are beginning to investigate whether the absorption of other colors of light, such as infrared, by skin molecules has a role to play in photodamage.
As research continues, one thing we know for certain is that protecting our DNA from UV damage, for people of every color, is synonymous with preventing skin cancers. The Skin Cancer Foundation, the American Cancer Society and the American Academy of Dermatology all stress that research shows regular use of an SPF 15 or higher sunscreen prevents sunburn and reduces the risk of non-melanoma cancers by 40 percent and melanoma by 50 percent.
We can still enjoy being in the sun. Unlike my Aunt Muriel and we kids in the 1980s, we just need to use the resources available to us, from long sleeves to shade to sunscreens, to protect the molecules in our skin, especially our DNA, from UV damage.
Hanson is a research chemist at the University of California at Riverside. This article was originally published on theconversation.com.
