Huulid

Huulid are the two fleshy folds that form the entrance to the mouth in humans and many mammals. They consist of skin on the outside, a subcutaneous layer, the underlying orbicularis oris muscle, and the mucous membrane lining the interior. The upper lip bears the philtrum, a vertical groove, and the vermilion border marks the transition to the skin. The border around the lips is the vermilion zone, often pigment-rich.

The lips receive blood from the facial artery via the superior and inferior labial arteries. Sensory innervation is provided largely by branches of the trigeminal nerve (for touch and temperature), with motor control by facial nerve branches that drive the orbicularis oris to close and compress the lips. The lips help seal the mouth, aid in speech and swallowing, assist in tasting and manipulating food, and contribute to facial expressions and nonverbal communication.

Lips vary in size, color, and shape among individuals and tend to become thinner with age. They are prone to drying, cracking, or inflammation (cheilitis) and are susceptible to infections such as herpes labialis or angular cheilitis. Lip aesthetics include cosmetics and, in some contexts, surgical augmentation.

In humans and many mammals, lips are multifunctional structures linked to feeding, communication, and protection of the oral cavity. Their appearance is influenced by genetics, nutrition, and environmental exposure.