When I was a kid, my sisters and I used to lie in the sun on the hood of my dad’s car. Three blonde girls in bikinis — skin slathered in Hawaiian Tropic, wreaking of the smell of coconut and commanding a colorful beach towel. If we didn’t make the Dean’s list, if we weren’t the most popular in school, even if we didn’t get asked to the dance, by god we had a brilliantly glowing tan.
Cut to twenty years later and one of us has been treated for skin cancer twice. Fair enough. We lived in the sun for hours every day. We spent entire days running around my Grandpa’s farm in cutoffs, bare arms and unprotected skin. At the lake, we covered ourselves in products that were essentially cooking oils. We didn’t cower in the shade or wear spf 70+. We were not surprised by a diagnosis of skin cancer.
We now know that Ultraviolet A (UVA) rays (from the sun or tanning beds) can cause damage to the DNA. But, what wasn’t knownuntil a new study in Science by Dr. Douglas Brash and his team at Yale University, was that even when we sat down under a tree in the shade to cool off, or went inside ending our day in the sun, the UVA rays continued to wreak havoc on our skin cells’ DNA.
Brash and his research team isolated skin cells from both mice and humans and exposed them to a UVA lamp. The researchers tracked genetic changes in the cells, discovering that changes continued to happen more than 3 hours after exposure to UVA light.
The melanin (the pigment that gives human skin, hair and eyes their color), which was thought to be the protective shield against UVA rays, turns out to also be the source for the damage post exposure to UVA rays. The UVA rays “excite” the melanin electrons, which then deposit the extra energy into the surrounding tissue. The melanin is acting in both good (protecting while in the sun) and harmful (affecting DNA) ways. This is a process Dr. Brash says has been seen in fireflies, but never in mammals.
We all have melanin, which ranges from black (eumelanin) to yellow (pheomelanin). Blondes and redheads have a higher ratio of pheomelanin to eumelanin in their hair and skin, which means a greater risk for melanoma (2 to 4 times higher) than dark-haired people. Dr. Brash’s study found that mice exposed to the UVA rays did not develop melanoma if they lacked melanin. However, mice with pheomelanin were 10 times more likely to develop melanomas.
So, melanin causes damage, but not as much as if it weren’t there at all, Dr. Brash says. “This situation is the best solution that evolution could come up with.”
While Dr. Brash’s work explains how pheomelanin production can be carcinogenic, he admits he does not know why we evolutionarily have melanin. Recent studies by Harvard professor, Hopi Hoekstra, can help with the answer. Prof. Hoekstra’s lab studied the selection on coat color in wild mice and found that variation in genes that regulate pheomelanin are repeatedly selected for both survival (blending into the environment) and sexual selection.
When humans stood upright and started shedding hair, their skin needed a pigment to protect it from the sun’s rays. And as the humans and their offspring began to move North, they shed some of that protection because they needed the sun’s rays to synthesize vitamin D. “Phoemelanin was an important part of the decorative toolkit of our forebears,” says Dr. Bruce Morgan, a skin biologist at Harvard Medical School. “Why do we still have it if it is so dangerous to our health? One could argue until recently the cumulative effects of extended UV damage were the least of our worries, as it was rare for us to survive until melanoma would occur, particularly before fair-skinned Northern Europeans started retiring to Florida.”
With more than 3.5 million cases of skin cancer diagnosed in the U.S. every year and Melanoma accounting for more than 73,000 of these cases, research into sunscreens and aftersun lotions continues. Brash’s team found Vitamin E lotions can slow the damage from melanin after tanning, but don’t help if applied before exposure.
In the end, nothing we have learned about protecting ourselves when in the sun has changed. We should continue to limit our time in the sun. Wear sunscreen. Get a hat. But, maybe add in some post-beach (or car hood) vitamin E lotion…just in case.
Interview with Dr. Douglas Brash, courtesy of Yale University