06/14/2009 05:12 am ET | Updated Nov 17, 2011

Dueling Docs - Does the Sun Really Cause Melanoma?

The Issue
Melanoma has always been considered linked to sun exposure, and sunscreen thought to protect against it. Now some doctors raise doubts.

The Facts
When most Americans think of melanoma, they think of John McCain as a POW baking in the Vietnam sun and developing such a severe form of the deadly skin cancer that his face was left scarred and oddly puffy. But is the sun really to blame?

Medical experts agree that sun can cause wrinkling, mottled pigmentation and generally age the skin, but now some researchers wonder if UV rays have anything to do with melanoma. They suggest there may not be a link, even though the rates of melanoma have gone up by 3.1 percent a year since 1992, coinciding with a thinning ozone layer. Indeed, this year, according to the National Cancer Institute, there will be 68,720 new cases of melanoma and 8,650 people will die from the disease. The risk of melanoma is more than 10 times higher for whites than for African Americans, particularly for fair-skinned Caucasians with red or blond hair who burn easily. Nevertheless, detractors say sunscreen won't do a thing to protect them.

Two doctors debate the issue. Sam Shuster, dermatologist and honorary consultant at Norfolk and Norwich University Hospital in the UK and Scott Menzies, dermatologist and associate professor at the University of Sydney, Sydney Melanoma Diagnostic Centre in Australia

The Debate

Dr. Shuster: "First of all, let's forget the politicians. It's rather arrogant for John McCain to make any assumptions about why he developed his melanoma. I'm surprised people believe anything politicians say anyway."

"All the scriptures about sun exposure and melanoma are premature. The UV explanation for melanoma is not adequate."

As evidence, Shuster says that "Melanoma cases occur on relatively unexposed sites of the body, especially the feet of dark-skinned Africans. There is no evidence that melanomas occur at sunburn sites on the body. Meanwhile, it's difficult to create melanomas in laboratory experiments with ultraviolet light, suggesting that UV has little impact."

Shuster acknowledges that the sun is responsible for some skin cancers, like basal and squamous cell, but, says he, "these are virtually benign and mostly trivial."

"Like smoking," says Shuster, "the sun makes the skin look as if it has been well lived in. But, there is no proof that ultraviolet light exposure is a significant cause of the rarer, truly malignant melanoma."

"If sun were important," he goes on, "we'd expect sunscreen to decrease the incidence of melanoma over the years as more and more people are using sunscreen. But that hasn't happened. Melanoma has actually increased."

Shuster suggests that the sun may actually decrease the risk of melanoma. "That's why we're seeing more melanoma cases in spite of the popularity of sunscreen. I have no hypothesis, but we do know that a substantial number of studies show an increased risk of melanoma with the use of sunscreen. Maybe the vitamin D from the sun protects against melanoma? All sorts of things are possible. There could be a bad fairy living in Mars, but that doesn't mean melanoma is related to sun exposure."

Does Shuster see a role for sunscreen then? "Well, we do know the sun makes us feel better, although we don't know how, and we do know that we need skin synthesis of vitamin D for our bones and that sun has important, unexplained immunological effects. But, if you burn and you live in a sunny environment and you want to use sunscreen, then go ahead."

Dr. Menzies: "To me this is a sort of flat-earth argument. Let's look at the real evidence here. It's true that in dark-skinned people, like the Asian and black populations, melanoma shows up in areas of the body that are not exposed to the sun and this certainly could suggest that melanoma is not related to UV light. In white-skinned races, we also see that 1% of melanomas are found in areas not-exposed to the sun. But in these cases, it's a different disease -- and a very rare one. What we do know is that melanoma is highly dependent on how much sun you get and your tendency to get sunburned. In the end, 95% of melanoma cases are due to sun exposure"

"To argue against this is like saying lung cancer is not caused by cigarettes because some people get lung cancer even though they don't smoke. It's exactly the same logic."

"We also know that the relative density or severity of the melanoma is greater on body sites that get more sun, like the trunk in men and lower extremities in women."

"Actually, the best predictor for melanoma is not total sun exposure, but hard and intermittent exposure that does the damage. Your cells don't develop adequate protections when your exposure is erratic."

"As for sunscreens, yes, it is correct to say that there is no evidence that sunscreens protect against melanoma. But there's a reason. People who wear sunscreens think they can spend more time in the sun and so they do. That's what increases their exposure to UV light and that's why sunscreens don't appear to be protective. Sunscreens are also used wrong all the time. To protect again melanoma and other skin cancers, sunscreen has to be applied properly. Apply a thick layer ½ hour before going out into the sun and reapply every two hours or after swimming or sweating. The higher the sunscreen, the greater the protection, so try to use a SPF of 30 or more."