Lip lines are fine vertical creases that form around the mouth, particularly above the upper lip in the area known as the philtrum. They develop from a combination of factors including sun exposure, repetitive muscle movement from talking and smiling, and the natural thinning of skin with age. Because these lines tend to trap makeup and cause it to feather or bleed, they are sometimes called smoker's lines or lipstick lines, though they occur in people with varying lifestyles.