Are you experiencing a dark upper lip after spending time in the sun? You may be on the receiving end of a "sun mustache." Every time you eat, sweat, rub your nose or take a drink, there's a chance that some of your sun protection is being wiped away with it. And when that area is exposed to the sun's damaging rays, it can result in a darker upper lip. To fix this, you need to be consistent with applying and re-applying sunscreen, and include skin brightening products in your skincare routine to improve uneven skin tone.