PITTSBURGH (KDKA) – We all know about the importance of sunscreen in preventing skin cancer.

But for some men, the risk of getting melanoma is doubled before they even set foot in the sun.

Melanoma is the most dangerous form of skin cancer. It turns out men who use Viagra have almost twice the risk.

“This study is worrisome,” said Dr. Brian Horvath with Horvath Dermatology.

About 25,000 male health professionals were followed for 10 years. During that time, researchers tracked which men developed Melanoma and whether they took Viagra.

The risk for melanoma was higher for those who were using the drug, or ever used the drug. Erectile Dysfunction itself was not linked to increased risk.

That doesn’t mean Viagra causes melanoma. It’s simply a statistical association the researchers noticed when they crunched the numbers.

Could there be other explanations?

“It may be that people who take Viagra are more likely to be out in the sun, or more active in some way,” said Dr. Horvath. “The problem with that idea though, is that the other types of skin cancer risks were not increased. So if was just sun exposure, you’d expect all skin cancers would increase. In this situation, just the melanoma risk was increased.”

So there is still the possibility it is the medicine. The reason researchers did the study is because the drug affects certain cell signals, similar to signals that allow melanoma cells to spread.

“Viagra blocks an enzyme called phosphodiesterase, and most melanomas have a mutation that also blocks that enzyme,” said Horvath.

At the time, the study was started, Viagra was the only FDA-approved medicine for ED. Since then, others, such as Cialis, Levitra and Stendra have come on the scene, which also block the same enzyme. We don’t know, but it’s possible similar patterns could be seen with these.

“The evidence is not firm,” said Horvath.

“If you’re thinking about going on Viagra, probably having a baseline skin check would be very reasonable,” he added.

He says if you have a melanoma to be cautious of taking Viagra.

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Dr. Maria Simbra