The study of nearly 60,000 post-menopausal women found those who used aspirin regularly were 21 percent less likely to be diagnosed with melanoma, while aspirin use for five years or more was tied to a 30 percent reduction in melanoma risk.
"These findings suggest that aspirin may have a chemopreventive effect against the development of melanoma," study author Dr. Jean Tang of Stanford University School of Medicine's Cancer Institute and colleagues wrote in their report, published today in the journal Cancer. "Further clinical investigation is warranted."
The study does not conclude that aspirin causes the drop in cancer risk -- only that twice-weekly use was associated with a decreased risk among Caucasian women in their 50s, 60s and 70s. It also relied on self-reports of aspirin use, and failed to control for a family history of melanoma and hair color. Redheads have a higher risk of skin cancer.
"This is one of many studies looking at the relationship between aspirin use and melanoma," said ABC News' chief health and medical editor Dr. Richard Besser. "Some have found an association between taking aspirin and having a lower risk of melanoma and some have not."
Aspirin, or acetylsalicylic acid, is an ancient painkiller dating back to 400 B.C., when people used salicin-containing willow tree bark to treat pain and inflammation. The drug also interferes with blood-clotting thromboxanes, leading some people take a daily dose to reduce the risk of heart attack and stroke.
The new study adds to mounting evidence that the over-the-counter staple may help prevent cancers of the colon, liver, breasts, lungs and skin. A May 2012 study found that men and women who used non-steroidal anti-inflammatory drugs or NSAIDs such as aspirin were 15 percent less likely to develop the non-melanoma skin cancer squamous cell carcinoma, and 13 percent less likely to develop malignant melanoma.
"This study builds on our knowledge of these medications being protective for the skin as well," said Dr. Josh Zeichner, assistant professor of dermatology at Mount Sinai Medical Center in New York City, who explained that aspirin's anti-inflammatory effects might be responsible for the drop in cancer risk. "We just don't yet know enough to make definite conclusions."
An NSAID cream is already approved for precancers of the skin caused by sun exposure. But experts say it's too soon to recommend aspirin for skin cancer prevention.
"The jury is still out," said Besser. "It's so important for people to remember that although you can buy aspirin over the counter, it is a real drug with significant side effects. It can increase your risk of having a stomach ulcer or a gastrointestinal bleed."
Until aspirin's cancer-fighting benefits are determined to outweigh the risks, there are easy steps anyone can take to lower their skin cancer risk.
"Right now the best way to prevent skin cancer is to use sunscreen, wear protective clothing and avoid of the sun between peak hours," he said.