Your daily Starbucks run may do much more than perk you up each morning and set you back five bucks. It may actually protect you from getting skin cancer.A new study backs up previous research that shows caffeine may be an effective weapon in the fight against skin cancer—the most prevalent type of cancer in the United States, according to the American Cancer Society.In the study, which was published in Proceedings of the National Academy of Sciences, two groups of mice—one genetically modified to block a certain protein called ATR, the other a control group—were exposed to ultraviolet (UV) radiation. The researchers found that the genetically-modified mice remained tumor-free for significantly longer and after 19 weeks of UV exposure, had nearly 70 percent fewer tumors than the control group.MORE: Green tea also has health benefits The research helps shed some light on how caffeine is able to decrease the risk of sunlight-induced skin cancer. Caffeine appears to inhibit the ATR kinase pathway, which plays a major role in how the body responds to DNA damage brought on by UV radiation. ATR obstructs cell division and allows DNA repair to occur rather than letting damaged cells die.This sounds like a good thing, but, “not all repairs are successful and some cells can still go on to develop cancer,” explains study co-author Allan Conney, the director of the Susan Lehman Cullman Laboratory for Cancer Research at Rutgers University School of Pharmacy. “The study we did with colleagues at the University of Washington identified the ATR kinase pathway as being inhibited by caffeine.” The result? More DNA damaged cells are killed off, potentially preventing non-melanoma (basal or squamous cell) skin cancer from ever developing.But caffeine doesn’t only inhibit this important protein. Caffeine itself also acts as a sunscreen, absorbing harmful UV rays, according to Conney. So will your sunscreen contain a shot of caffeine one day? “I would think that’s a real possibility,” he says.QUIZ: How healthy is your skin?Until that day comes, there’s some good news for coffee drinkers: You’re already getting some sun protective benefits from your daily cup of joe. A 2007 study of nearly 94,000 women found that those who sipped caffeinated coffee daily had an almost 11 percent lower risk of non-melanoma skin cancer. Women who drank six or more cups of coffee on a daily basis saw a 30 percent reduction in risk.(To put that in perspective, a venti size at Starbucks is two and a half cups of coffee.)Just don’t skip the sunblock. “Let’s put it this way—you shouldn’t start depending on your local Starbucks for sun protection,” says Dr. Howard Sobel, a cosmetic dermatologist in Manhattan. “The same general rules apply when it comes to sun protection. Apply a broad-spectrum, water-resistant sunscreen with a SPF of 30 or more to all exposed skin. Look for broad-spectrum on the label, as it provides protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Reapply every two hours, even on cloudy days, and after swimming or sweating. Avoid tanning beds, and have your skin checked regularly by a dermatologist.”