By Lisa Marshall

Your favorite gloss may be the ultimate summer must-have, but research shows that shimmery lip balms and glosses can actually boost the risk of lip cancer by allowing ultraviolet rays to penetrate more deeply.

“When light shines on dry or rough skin, it scatters,” says Theresa Pacheco, MD, associate professor in the department of dermatology at the University of Colorado at Denver. “If your skin is nice and smooth—like it is after you’ve applied a shiny gloss—the rays will theoretically be absorbed.”

But this doesn’t mean you should skimp on lip protection. Studies show that only about 25 percent of us use lip balms with sunblock, even though doing so more than once a day can cut lip cancer risk in half. Lip cancer can be particularly insidious, say dermatologists, because if left untreated, it can spread inside the mouth and also lead to potentially disfiguring surgery.

“When skin cancer occurs on the lower lip, it has the potential to be much more aggressive and metastasize to surrounding lymph nodes,” says Christine Brown, MD, a dermatologist at Baylor University Medical Center in Dallas.

Signs of lip cancer include a lip sore or white, flaky patch that will not heal; a thickening of the lips; or consistent numbness, pain, or bleeding. Dermatologists recommend applying a lip-protection formula of SPF 15 or higher in the morning (even if it goes beneath that gorgeous gloss). Or better yet, find a lipstick that contains sunscreen. Quick tip: Many sunscreens contain chemicals that have been linked to hormone disruption or nanoparticles (often present in titanium dioxide and zinc oxide products) that have been linked to DNA damage. To be on the safe side, look for an SPF lip balm that is both nanoparticle- and chemical-free (Jason Natural Products and Alba Botanica both carry such products).