The vermilion border is the line along the outside of the lips where they join the skin of the face. It may be a distinctive line, especially in Caucasians and light-skinned people. The definition of vermilion is "brilliant scarlet or red." While the vermilion border of the lips differs from person to person, it is not normally scarlet or red, but may be slightly darker than the rest of the lips. The red color of the lips is due to the skin being thinner in that particular area than in the rest of the face, and the area being well supplied with blood vessels.
Unlike the skin surrounding them, the lips, including the vermilion border, do not have any sebaceous glands, sweat glands or hair follicles. This may explain why lips tend to dry out, especially during the wintertime, far more easily than does the rest of the face, despite everything being exposed to exactly the same environmental factors. The sebaceous glands on the rest of the body secrete sebum, a slightly waxy substance that is believed to be involved with preventing dehydration of the skin.
A number of diseases may occur at the vermilion border, the most well known being herpes simplex, a highly contagious, recurring disease commonly known as cold sores. Small blisters develop on the lip, usually along the outer edges, which can heal slowly by themselves or may require topical or systemic treatment. Another condition occurring on the outer edges of the lips is angular cheilitis. This is a drying or chapping in the outer corners of the mouth that may, in severe cases, cause splitting of the lip.
The vermilion border is involved in a number of cosmetic procedures. Lip tattooing is one. This is a process that involves tattooing the lips to allow a permanent deepening of their color. Some people opt to tattoo only the vermilion border, giving a permanent lip liner effect. In some cases, people may tattoo around the outer edge of the vermilion border to broaden the lips. All of these procedures should only be performed by a trained professional and under sterile conditions.