Is sunscreen ineffective in preventing skin cancer?

Dear Cecil:

We have been taught to slap on sunscreen to prevent skin cancer. Recently I have come upon a number of references suggesting that our commonly used sunscreens may not be effective at all in preventing melanoma but only in preventing more common but also more benign and treatable skin cancers. Is this true? If so, who is behind the sunscreen lobby? Thanks in advance for letting your light shine on this.

Cecil replies:

Little late in the summer to be bringing this up, but maybe now you’ll have something to read in the waiting room at the cancer specialist’s. The scariest version of this story is that sunscreen increases your chances of getting cancer. More on that in a mo. But first let’s answer your question. There’s no hard evidence that sunscreen prevents melanoma, the least common but most dangerous skin cancer (42,000 cases per year, and 7,000 deaths), or even basal cell carcinoma, the most common, least dangerous cancer (600,000 cases a year, rarely fatal). Sunscreen prevents sunburn and possibly squamous cell carcinoma (200,000 cases, perhaps 2,000 deaths). More than that we just don’t know.

Back to the scary version. Here’s the case against sunscreen as presented by Michael Castleman in Mother Jones (http://www.motherjones.com/politics/1994/01/sun-signsl): (1) Melanoma was rare before 1950 but subsequently rose to epidemic proportions and now is increasing at a rate of 6 percent annually. (2) Increased sunbathing and the thinning ozone layer can’t possibly account for all this. (This is more asserted than proved; I haven’t seen scientific studies making these arguments.) (3) Sunscreen use, as measured in sales revenue, rose sharply after 1970. Lifetime melanoma risk increased sharply during roughly the same period. (4) Sunscreens protect against UV-B rays, the primary cause of sunburn, but are less effective against UV-A rays, which penetrate more deeply and, some think, cause melanoma. (5) Sunscreen thus defeats your natural early-warning system against excessive sun exposure — sunburn. Since you don’t burn, you stay out longer, and next thing you know you’ve got a skin tumor the size of Oahu.

Sunscreen critics got a boost in February 1998, when epidemiologist Marianne Berwick of the Memorial Sloan-Kettering Cancer Center in New York told a scientific conference that of ten studies she’d reviewed (including one of her own), two found that sunscreen had a preventative effect, three found no effect, and five found that sunscreen actually increased the risk of melanoma. (Two subsequent studies likewise came to opposite conclusions.) Berwick also questioned the belief that having had three or more instances of severe sunburn before age 18 is a predictor of melanoma — people’s memories of such incidents are too unreliable to permit generalizations, she found.

Berwick took a lot of heat, but most of it was harrumphing by guys who didn’t like her calling their bluff. Fact is, we don’t know much about the causes of melanoma, mainly because of a lack of “animal models” to study — few suitable lab animals get skin cancer solely due to UV exposure, as humans seem to. Because of that, we can’t offer much in the way of definitive statements or useful advice. Having spoken to Berwick and to Frank Gasparro, a dermatology professor and sunscreen expert at Thomas Jefferson University in Philadelphia, I can offer only these crumbs:

  • Genetics are the major factor in melanoma. You’re at twice the risk for melanoma if you’re a sun worshipper, but six times the risk (acccording to Berwick) if you’re fair-skinned or have lots of moles. If you’re of northern European extraction (Celtic in particular), or if you’re prone to freckles, get sunburned easily, or have light-colored hair or eyes or a family history of skin cancer, keep sun exposure to a minimum or you’re toast. The Australian state of Queensland, whose inhabitants are predominantly Anglo-Saxon, has the highest melanoma rate in the world. An estimated two out of three Australians will be treated for skin cancer by age 75. One disconcerting fact: some melanomas aren’t caused by sunlight at all.
  • If you’re black, you get a break. Skin cancer risk in whites is 70 times higher than in African-Americans.
  • Don’t shun sunscreen. It does prevent sunburn, after all. (Berwich and Gasparro don’t buy the sunscreen = cancer theory. Too many unknowns.) But don’t make it your sole line of defense. Minimize your solar exposure, particularly during peak hours, 10 AM to 4 PM (Too much to ask? Make it 11 to 2.) Wear wide-brimmed hats, clothing that doesn’t leave much skin exposed, and sunglasses. Avoid tanning parlors. Protect kids and infants.
  • If you have Mediterranean-type skin (tans easily), and you feel you must get a tan, do so gradually but steadily. The increased pigment production and thickened skin may offer some protection against melanoma, which is associated with intermittent (e.g., only weekend) exposure to sun. This is controversial advice; some feel a tan is bad for you, period.
  • Check out sunscreens containing zinc oxide, titanium dioxide, or avobenzone. Though not easy to come by, these are among the few commercially available ingredients known to protect against UV-A. Which doesn’t necessarily cause melanoma, I hasten to say, but might. When we know so little about skin cancer, no sense leaving anything to chance.

Send questions to Cecil via cecil@straightdope.com.

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