On Wednesday, the Indoor Tanning Association ran a full-page ad (PDF) in the New York Times claiming that "there is no compelling scientific evidence that tanning causes melanoma." It went on to say that "recent research indicates that the benefits of moderate exposure to sunlight"—namely, increased levels of vitamin D—"outweigh the hypothetical risks." Wait, is sunbathing good for you?
Only for a few minutes. Exposure to sunlight (or the UV lamps in a tanning bed) does cause the skin to produce vitamin D, which has a host of salubrious benefits, including the maintenance of normal blood levels of phosphorus and calcium and the promotion of healthy bones. Studies have shown that many segments of the population aren't getting enough of the vitamin, which may even aid in the prevention of cancer, diabetes, and HIV. According to almost all experts, most people could cover their bases by getting just five to 15 minutes of sunlight two to three times a week. (You'll need a little more if you're darker-skinned, a little less if you live near the equator.) Supplements are also an option. So even the palest sun worshipper doesn't need to get a tan for a vitamin fix.
So, does tanning cause melanoma? First, to be clear, it isn't tanning that's the problem—it's the sun exposure that causes both the suntan and, as most dermatologists believe, the cancer.
Second, there are two kinds of skin cancer: melanoma and nonmelanoma. Nonmelanoma skin cancers, by far the more common variety, usually aren't fatal, though their removal can be painful and cause scarring. Because these lumpy, scaly areas usually appear on parts of the body that get regular sun exposure, and because they are found on outdoor workers more frequently than on indoor workers, most doctors assume that solar radiation is a leading cause of nonmelanoma cancer.
Melanoma is the deadlier of the two, responsible for 4 percent of skin-cancer diagnoses but 75 percent of all skin-cancer deaths. Most doctors believe that excessive exposure to the sun (even in relatively short, intense bursts) and, consequently, to UV radiation are the major risk factors for melanoma. Studies have shown that the more sunburns you've had in your life, the higher your chance of developing the disease. However, the exact causes of the disease aren't fully understood. People who doubt the sun-cancer link point to the fact that melanoma can sometimes appear in areas that get zero sun exposure, such as the bowels and the soles of the feet. They also note that melanoma is more common among indoor than outdoor workers, though other doctors counter that this is because cubicle dwellers are more likely to go on vacations where they spend hours baking in the sun.
Along with its full-page ad, the Indoor Tanning Association submitted a letter to the Times that attempted to substantiate the health claims, sentence-by-sentence. However, the evidence provided is rather selective: For example, the paper from the Proceedings of the National Academy of Sciences that the ITA uses to provide sole support for its claim that "the benefits of moderate exposure to sunlight outweigh the hypothetical risks" also concedes that "solar radiation is the main cause of skin cancers." Meanwhile, indoor tanning isn't any safer than outdoor sunbathing—in fact, the FDA notes that it may be more dangerous, since tanning-bed users expose their entire bodies at once to a uniform amount of UV radiation. The American Academy of Dermatology has called for a ban on all indoor tanning equipment used for nonmedical purposes.
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Explainer thanks Marie-France Demierre of the Boston University School of Medicine, and Sarah Longwell and Justin Wilson of the Indoor Tanning Association.