Lips

Lips are the two fleshy folds surrounding the mouth, consisting of an externally located skin that is thin and hairless, a transition zone called the vermilion border, and an inner mucous membrane that lines the oral cavity. The upper and lower lips join at the midline and meet the philtrum above the cupids bow in the upper lip. The lips contain the orbicularis oris muscle, which helps seal the mouth and shape speech, and the vermilion region is highly pigmented due to the underlying vascular network.

The lips receive arterial blood from the superior and inferior labial arteries, branches of the facial artery. Sensation is provided by branches of the trigeminal nerve: the upper lip mainly by the superior labial nerves (V2 via the infraorbital branch) and the lower lip by the inferior labial nerves (V3 via the mental nerve). Motor control for lip movement is provided by the facial nerve, via its buccal and other branches to the orbicularis oris.

Functions of the lips include aiding in speech articulation, food processing, and creating a seal to prevent spillage while eating. They are also important for facial expression and social communication. Common conditions affecting the lips include cheilitis (inflammation of the lips), angular cheilitis at the corners, and herpes labialis (cold sores) caused by herpes simplex virus. Lips can become dry, cracked, or irritated from environmental exposure or irritants, and may be affected by allergic dermatitis or infections.

Developmentally, the lips arise from embryonic facial prominences, with natural variation in size, shape, and color among individuals. Cosmetic procedures such as lip augmentation with fillers or tattooing are used in some cases. Lip prints have forensic value in identifying individuals, reflecting their unique patterns.