Smegma

Smegma (from Ancient Greek σμῆγμα, smêgma, 'soap') is a cheesy substance composed of shed skin cells, skin oils, and moisture that occurs in male and female mammalian genitalia. In males, smegma collects under the foreskin; in females, it collects around the clitoris and in the folds of the labia minora.

Females

The accumulation of sebum combined with dead skin cells forms smegma. Smegma clitoridis is defined as the secretion of the apocrine (sweat) and sebaceous (sebum) glands of the clitoris in combination with desquamating epithelial cells. Glands that are located around the clitoris, the labia minora, and the labia majora secrete sebum.

If smegma is not removed frequently it can lead to clitoral adhesion which can make clitoral stimulation (such as masturbation) painful (clitorodynia).

Males

In males, smegma helps keep the glans moist and facilitates sexual intercourse by acting as a lubricant.

Smegma was originally thought to be produced by sebaceous glands near the frenulum called Tyson's glands; however, subsequent studies have failed to find these glands. Joyce Wright states that smegma is produced from minute microscopic protrusions of the mucosal surface of the foreskin and that living cells constantly grow towards the surface, undergo fatty degeneration, separate off, and form smegma. Parkash et al. found that smegma contains 26.6% fats and 13.3% proteins, which they judged to be consistent with necrotic epithelial debris.