The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans.

[1] Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. suckling and gulping) and the articulation of sound and speech.

Human lips are also a somatosensory organ, and can be an erogenous zone when used in kissing and other acts of intimacy.

Therefore, it does not have the usual protection layer of sweat and body oils which keep the skin smooth, inhibit pathogens, and regulate warmth.

The muscles of facial expression are all specialized members of the panniculus carnosus, which attach to the dermis and so wrinkle or dimple the overlying skin.

Functionally, the muscles of facial expression are arranged in groups around the orbits, nose, and mouth.

In addition, lips serve to close the mouth airtight shut, to hold food and drink inside, and to keep out unwanted objects.

The lips serve for creating different sounds—mainly labial, bilabial, and labiodental consonant sounds as well as vowel rounding—and thus are an important part of the speech apparatus.

The lips enable whistling and the performing of wind instruments such as the trumpet, clarinet, flute, and saxophone.

People who have hearing loss may unconsciously or consciously lip read to understand speech without needing to perceive the actual sounds, and visual cues from the lips affect the perception of what sounds have been heard, for example the McGurk effect.

It has been shown that the more oestrogen a woman has, the larger her eyes and the fuller her lips, characteristics which are perceived as more feminine.

Women are attracted to men with masculine lips that are more middle size and not too big or too small; they are to be rugged and sensual.

In general, the researchers found that a small nose, big eyes and voluptuous lips are sexually attractive both in men and women.

[12] Possible reasons for the difference may include advantages to somatosensory function, better communication of facial expressions, and/or emphasis of the lips' slight sexual dimorphism as a secondary sex characteristic.

However, in mammals, they become much more prominent, being separated from the jaws by a deep cleft[citation needed] (a notable exception being the naked mole-rat, whose lips close behind the front teeth).