Labium and its derivatives (including labial, labrum) are used to describe any lip-like structure, but in the English language, labia often specifically refers to parts of the vulva.
The labia majora are lip-like structures consisting mostly of skin and adipose (fatty) tissue, which extend on either side of the vulva to form the pudendal cleft through the middle.
The outer surface of the labia majora is pigmented skin, and develops pubic hair during puberty.
The labia majora have fewer superficial nerve endings than the rest of the vulva, but the skin is highly vascularized.
[6] The internal surface of the labia minora is a thin moist skin, with the appearance of a mucous membrane.
They can range in color from a light pink to brownish black,[8] and texturally can vary between smooth and very rugose.
The genital tissues are greatly influenced by natural fluctuations in hormone levels, which lead to changes in labia size, appearance, and elasticity at various life stages.
[6]During early childhood, the labia majora look flat and smooth because of decreasing levels of body fat, and the diminished effects of maternal hormones.
The labia majora regain fat, and begin growing pubic hair close to the pudendal cleft.
Hair is initially sparse and straight, but gradually becomes darker, denser, and curlier as growth spreads outward and upward toward the thighs and mons pubis.
[7] Later in life, the labia majora once again gradually lose fat, becoming flatter and more wrinkled, and pubic hair turns grey.
The labia minora become engorged with blood, causing them to expand in diameter by two to three times, and darken or redden in color.
[12] Because pregnancy and childbirth increase genital vascularity, the inner and outer labia will engorge faster in women who have had children.
[12] After a period of sexual stimulation, the labia minora will become further engorged with blood approximately 30 seconds to 3 minutes before orgasm,[12] causing them to redden further.
[17] In several countries in Africa and Asia, the vulva is routinely altered or removed for reasons related to ideas about tradition, purity, hygiene and aesthetics.
Known as female genital mutilation, the procedures include clitoridectomy and so-called "pharaonic circumcision," whereby the inner and outer labia are removed and the vulva is sewn shut.