The labia majora (singular: labium majus) are a pair of rounded folds of skin and adipose that are part of the external female genitalia. Their function is to cover and protect the inner, more delicate and sensitive structures of the vulva, such as the labia minora, clitoris, urinary orifice, and vaginal orifice. The word “labia” comes from the Latin word for lips, which corresponds to the function of the labia majora surrounding the vaginal orifice like lips surround the mouth. The labia majora are homologous to the scrotum in males and develop from the same embryological tissue.
The labia majora are located in the pubic region on the surface of the body lateral to the labia minora, clitoris, and vagina. They arise gradually from the skin of the pelvis and extend the mons pubis beyond the pelvic bones to the anus. Adipose tissue deep to the skin supports the labia majora and provides cushioning and flexibility to the pubic region. Together, the labia majora form the lateral borders of the pudendal cleft, the vertical fissure of the vulva. Anterior to the pudendal cleft, they join to form the anterior commissure of the labia majora, just inferior to the mons pubis. On the posterior end, the labia majora gradually merge with the surrounding skin in the perineal region at their posterior commissure.
The major function of the labia majora is protection of the softer tissues of the vulva. Unlike the inner structures of the vulva, the labia majora contain many pubic hairs that help to protect the rest of the vulva from mechanical stress and friction. The adipose tissue of the labia majora also helps to cushion the vulva from exterior stresses. Many exocrine glands are associated with the hair follicles of labia majora, including apocrine sudoriferous glands, eccrine sudoriferous glands, and sebaceous glands. Eccrine sweat glands assist in thermoregulation by producing watery sweat, while sebaceous glands produce oil to lubricate the hair shafts and skin. Apocrine sweat glands produce a fatty secretion that is consumed by bacteria living on the skin, producing a particular form of body odor. It is believed that the odor produced by apocrine sweat glands once acted as a pheromone to attract mates.