Health experts have been wondering for a while just how effective sunscreens are at protecting the skin from harmful ultraviolet rays.
Now, some are wondering if chemicals in the lotions might actually cause cancer when they’re exposed to the sun over long periods.
Dr. Yinfa Ma, professor of chemistry at Missouri University of Science and Technology, and his graduate student Qingbo Yang, recently studied how human lung cells react when they are immersed in a solution containing zinc oxide, then exposed to different types of light over numerous time frames. Zinc oxide is the active ingredient found in many sunscreens.
What they found, Ma says, is that when zinc oxide’s nano-particles were exposed to sunlight, they released unstable molecules, called free radicals. Free radicals can damage cells or the DNA contained within those cells, which, in turn, could increase the risk of skin cancer.
They also found that the longer zinc oxide is exposed to sunlight, the greater the potential for damage to human cells. Specifically, they found that when the lung cells that had been immersed in the zinc oxide solution were exposed to ultraviolet A rays for three hours, half of them died. After 12 hours, 90 percent died.
Two weeks ago, Ma says, “we further confirmed our discovery when we traveled to Washington University and collaborated with researchers there using electron spin resonance.” The scientists, he said, found a much higher concentration of free radicals than in previous tests.
Skin cancer is the most common form of cancer in the United States. The Skin Cancer Foundation estimates that one in five people will be diagnosed with skin cancer in their lifetime; more than 2 million people are diagnosed each year. Between 40 percent and 50 percent of Americans who live to age 65 will have it at least once.
Last year, after hearing concerns from health experts about the effectiveness of sunscreen, the Food and Drug Administration issued a statement that said, “to date, there are no clinical studies demonstrating that use of any sunscreen alone can prevent skin cancer.”
The FDA also issued new rules last year prohibiting sunscreen manufacturers from labeling their products as waterproof, sweat-proof or sun blocks. And sunscreens that are not broad spectrum or that have SPF values between 2 and 14 must be labeled with a warning that reads: “Skin Cancer/Skin Aging Alert: Spending time in the sun increases your risk of skin cancer and early skin aging. This product has been shown only to help prevent sunburn, not skin cancer or early skin aging.”
Several studies over the years have found that sunscreen, when used frequently, appears to lower the risk of squamous cell carcinoma and basal cell carcinoma, both non-melanoma cancers that are slow-growing and almost never lethal.
But the studies also found mixed results on whether sunscreen prevents melanoma, the most deadly form of skin cancer.
To fully protect yourself, health experts highly recommend using a multi-prong approach that includes using sunscreen, staying in the shade and wearing wide-brim hats and sun protective clothing over most of the body.
As for sunscreen actually causing cancer, Ma warns that you should not throw out that bottle just yet.
“These are very preliminary studies,” he said.
He’s applying for funding from the National Institutes of Health to perform similar studies using skin cells rather than lung cells.
It’s possible, he noted, that other chemicals in sunscreens minimize the cancer or absorb the free radicals, and he intends to look at that, too.
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