There is new evidence that the sun’s UV rays are even more damaging than previously thought.
The sun emits two kinds of UV rays to the earth’s surface: UVA and UVB. It had been thought that those rays do not damage the deeper layers of the skin as much as they damage the top layers. New research from Kings College London has found that is the case for UVB rays, but not for UVA rays. The study has found UVA rays are more carcinogenic than previously realised – a finding scientists say underscores how important it is to limit exposure to the sun and to tanning studios. The study was led by Antony Young, Professor of experimental photobiology at King’s College.
“The damage seemed to increase as it went through the epidermis and we think that is due to a form of backscatter in other words, the damage goes through and is somehow reflected back,” he said.
That is significant because the deepest layer of the skin, the basal layer, is where cells divide, dividing cells or cells that divide to produce the rest of the epidermis, if they carry mutations that has possible consequence in terms of skin cancer. We must try to protect the basal layer,” Professor Young said.
The research suggests that UVA rays are more carcinogenic than previously realised.
UVA rays are further divided into UVA1, the rays with the lowest energy that account for about 75% of visible sunlight, and UVA2. UVA is also the main kind of radiation used in tanning beds.
“People have really not been that concerned with UVA1 in the past. They’ve been more concerned, in the UVA spectrum, UVA2, which is closer to UVB,” says Darrell S. Rigel, MD, a clinical professor of dermatology at New York University Medical Center. A new study by Rigel shows that “with the UVA1 they were able to produce the same types of DNA damage that you see in early skin cancer, and that’s actually interesting because that hasn’t really been shown before,” says Rigel, who was not involved in the research.
The findings make it even more important, experts say, for people to regularly use broad spectrum sun protection, from hats, sun-protective clothing, and sunscreen. That isn’t always an easy task since the sun protection factor (SPF) listed on sunscreen labels only measures how well the product blocks UVB, not UVA.
“The issue right now is that there’s no easy way for me to tell my patients how to get good UVA protection in sunscreen,” Rigel said.
For the study, which is published in the Journal of Investigative Dermatology, researchers recruited 12 volunteers who had never sunbathed or used tanning beds while naked. They exposed skin on their buttocks, which tends to be the least sun-exposed part of the body, to UVB and UVA1 radiation. The light was applied just long enough, in each case, to cause the skin to burn. Researchers then cut away a small area of the burned skin and looked for DNA damage in the cells.
The kind of damage they saw in UVA exposed skin has been shown in other studies to lead to skin cancer. UVA causes these changes at a larger incidence than has been expected or predicted, researchers say.
“These particular lesions are repaired quite slowly. And so even if you get small doses, but get them on a daily basis, the damage builds up,” says study researcher Antony R. Young, professor of experimental photobiology at St. John’s Institute of Dermatology at Kings College London.
“The amount of damage with UVA actually increases as you go more deeply into the skin, and I think that’s due to some kind of reflection process of UVA so it goes in and then it’s sent back,” he says.
“I see this as a marker of UVA penetration,” Young says. If it’s that deep in skin “it may cause other types of damage, like oxidative damage, which we didn’t measure but which are thought to be important in cancer in general.”
His findings, Young says, “support a role for UVA protection in sunscreen.” Right now, he says, sunscreens in the U.S. don’t protect as well against UVA as they do against UVB. But new FDA regulations set to go into effect next summer could spur sunscreen makers to increase UVA protection in their products.