With summer sun shining brightly across the United States (at least on most days), there is no better time to review the latest sobering findings on the damage that ultraviolet radiation can inflict on one’s skin and then take steps to prevent it.
A British research team reported in May in the journal Science that a quarter or more of cells in the skin of middle-aged people have suffered sun-induced DNA damage. Although the cells were outwardly normal, the mutations that occurred could be the first stages of cancer.
The researchers, led by Peter J. Campbell, a cancer geneticist at the Wellcome Trust Sanger Institute in England, examined the eyelid skin of four middle-aged adults — three were Western European and one was of South Asian descent — and found that hundreds of ostensibly normal cells had mutations linked to cancer, a number “way higher than we’d expect,” Campbell said. Clusters of these mutant cells, called clones, appeared in every 0.1 square inch of skin, with thousands of DNA mutations in each cell.
Although it is not known if the same rate of mutations occurs in sun-exposed skin elsewhere on the body, or in people of different ethnic backgrounds, or even how many of the mutations would progress to cancer, it is not a finding to dismiss lightly.
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Douglas E. Brash, a biophysicist at Yale University School of Medicine who has studied ultraviolet damage to cells for more than 40 years and wrote a commentary on the British study, described the new findings as “a canary in a coal mine” and a warning to take the effects of ultraviolet radiation, whether from sunlight or tanning beds, more seriously.
It is especially important, he said, “to be very conscientious about protecting young children,” who are more susceptible than teenagers and adults to ultraviolet-induced mutations.
“A lot of damage occurs when people go to the beach,” Brash said. “While the body does a great job of repairing the damage and gets 99.9 percent of things right, every once in a while, you do get a mutation that may make a cell resistant to death, allowing it to form a clone that can become a cancer.”
Complicating the matter is that many people don’t understand the meaning of the SPF rating listed on modern sunscreens — only 43 percent of 114 people surveyed at a dermatology clinic in Illinois last summer, according to a study in JAMA Dermatology. The rating, which stands for sun protection factor, is meant to reflect how well a product protects against sunburn, which should also reduce the risk of skin cancer and sun-induced skin aging. And less than a third of people use sunscreen regularly, according to the Centers for Disease Control and Prevention.
Dermatologists have long cautioned people not to rely too heavily on sunscreens, even products with the recommended SPF rating of 30 or higher for summer sun protection. Few people who do use sunscreen use enough to achieve the level of protection measured in the laboratory, and few reapply it often enough. A better plan is to stay out of the sun, especially midday, and cover the skin when sun exposure is unavoidable.
Furthermore, a recently published study by Brash’s team at Yale showed that much of the harm to skin cells caused by ultraviolet radiation occurs hours after the exposure has ended. Even in the dark, substances formed during UV exposure continue to damage melanin, the pigment that gives skin its color, “exciting electrons, the energy from which gets transferred to DNA and can damage it in the same way that UV photons do,” Brash explained.
In its latest analysis of 1,000 commercially available sunscreens, the Environmental Working Group, a consumer advocacy organization based in Washington, rated sunscreens made with zinc oxide or titanium oxide high because “they provide strong sun protection with few health concerns” and “they don’t break down in the sun.” These substances are also more protective than other sunscreen ingredients against UVA rays, which can cause aging of the skin and immune suppression and characteristic sun-induced mutations in skin cells. The group’s complete 2015 sunscreen guide is available online at ewg.org/2015sunscreen.
Some consumers erroneously believe that choosing a more expensive sunscreen with a sky-high SPF number like 70 or 100 will provide complete protection. However, the Food and Drug Administration has not determined that an SPF of more than 50 has any added benefits.