Lip

Lips are one of the most visible of all human organs and maybe the most expressive part of the human body. They have multiple functions, they provide an opening for food and beverage consumption, they allows us to communicate, they’re a tactile sensory organ and an erogenous zone.

The upper lip (Labium superius) is different from the lower lip (Labium inferius); the lower lip is usually larger. Lips are composed of skin, muscle and mucosa. The border between the lips and the surrounding skin is referred to as the vermilion border. This colored border between the lips and the surrounding skin exists only in humans. The vertical groove on the upper lip, that forms the so-called “Cupid’s Bow” is known as the philtrum. The skin of the lip, with 3 to 5 cellular layers, is very thin compared to typical face skin, which has up to 16 layers.

The mucous membrane of the lip is full of capillaries (tiny blood vessels) that are close to the translucent surface, giving it a reddish color. With darker skin color this effect is less prominent. The lip skin is not hairy, and does not have sweat glands or sebaceous glands. The lips are also somewhat fragile when compared to other areas of skin on the body. They lack the usual protective layer of body oils that keeps skin smooth. That's why lips tend to dry out faster and become chapped more easily, most times in the winter. Lips are controlled by their own muscles, which make part of the muscles of facial expression. Mainly the muscles acting on the lips are the sphincters of the oral orifice, modiolus, muscles that raise the lips and muscles that lower the lips. The principal lip muscle is the orbicularis oris.

The lip movement is directed by the orbicularis oris and by the muscles in the upper and lower lips, making them extremely expressive as well as multi-functional. Lips are used for eating functions, like holding food or to get it in the mouth. And also a eating function is the basic one, that allows babies to breastfeed or suck from a bottle. Infants use their lips not only to suck, but to explore their world. As they grow older, lips emphasize their changing range of emotions like no other body part can, from anger to joy, laughter to crying. The lips serve for creating different sounds. They allow talented people to play musical instruments such as the trumpet, clarinet, panpipe. Lips are very sensitive to touch, warmth, and cold, as part of the tactile sense. Having a high number of nerve endings, the lips are considered to be an erogenous zone, playing a crucial role in kissing and other acts of intimacy.

Lips are a very important part of our body, so important and so unique, that human lips recognition is to be one of the most interesting emerging methods of human identification.