The first thing to know about angular cheilitis is that it’s perfectly normal. The condition is so common, in fact, it’s taught on day one of dermatology school, says S. Manjula Jegasothy, M.D ., a Miami-based dermatologist. That’s because these annoying little sores stem from something as simple as drool (which, of course, is something we all do — and not just over the brothers Hemsworth). “Yeast is always present in the mouth and saliva, so when we drool in our sleep, it collects in the corners of the mouth, like rain in a gutter,” Dr. Jegasothy explains. This buildup of yeast causes dry, red flakes of skin to form. “Because the grooves in the corners of our mouth get deeper as we age, this can worsen the older we get,” she says.