Lips

Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be erogenous when used in kissing and other acts of intimacy.

Anatomical basics of the human lip

One differentiates between the upper (Labium superius) and lower lip (Labium inferius). The lower lip is usually somewhat larger. The border between the lips and the surrounding skin is referred to as the vermillion border, or simply the vermilion. The vertical groove on the upper lip is known as the philtrum.
The skin of the lip, with three to five cellular layers, is very thin compared to typical face skin, which has up to 16 layers. With light skin color, the lip skin contains fewer melanocytes (cells which produce melanin pigment , which give skin its color). Because of this, the blood vessels appear through the skin of the lips, which leads to their notable red coloring. With darker skin color this effect is less prominent, as in this case the skin of the lips contains more melanin and thus is visually darker. The skin of the lip forms the border between the exterior skin of the face, and the interior mucous membrane of the inside of the mouth.

The lip skin is not hairy, and does not have sweat glands or sebaceous glands. Therefore it does not have the usual protection layer of sweat and body oils which keep the skin smooth, inhibit pathogens, and regulate warmth. For these reasons, the lips dry out faster and become chapped more easily.