Smegma is a natural, cheese-like substance that accumulates under the prepuce, or the foreskin in men and under the clitoral hood in women. The exact contents of these subpreputial accumulations are debated amongst scientists, though it certainly contains desquamated epithelial cells, or dead skin cells. The color can be white to yellow, depending on the person’s skin pigments, and it has a distinctive odor.
In women, smegma builds up in the folds of the labia minora, around the clitoris. This area is sometimes called the clitoral hood, because the skin of the labia minora forms a hood-like covering over the clitoris, or the small, round protrusion in front of the urethral opening. The build-up may be moist or dry and can be washed away with water. It is a perfectly normal secretion in healthy women, made up of a combination of shed skin cells and sebum, a natural, oily lubricant secreted by the glands around the vulva and clitoris.
In men, the composition of this substance is still largely unknown, though it certainly contains dead skin cells. Male subpreputial collections may also contain sebum in early years, though not later in life, as well as secretions from the penis, and perhaps urethral gland secretions. At one point in time, it was alleged that structures called Tyson’s glands were producing sebum that contributed to the collection, but this has since been debunked.
Subpreputial collections have played a large role in the circumcision debate, mostly for men, but also for women in parts of the world. They are more prevalent in uncircumcised males and have often been associated with poor hygiene, disease, and an undesirable smell. For this reason, along with aesthetic and other purposes, male circumcision has become an accepted practice.
Many, however, argue against using smegma as reasoning for circumcision, as there is no evidence that it increases the risk of disease, and simply washing with water can remove the build-up and its odor. This substance also benefits sexual function, acting as a natural lubricant to allow the painless movement of the foreskin up and down over the glans, or head, of the penis. Some have also alleged that subpreputial collections may have antibiotic and cleansing properties. This has not been proven in humans, though it is true for other mammals.
Smegma tends to increase with age and, for most people, presents no problems. Most problems with infection stem from poor hygiene, unrelated to subpreputial wetness. Washing with warm water can solve problems of build-up, but too much washing, especially with harsh soaps, can cause dermatitis. Thick secretions from the vagina and penis are unlikely to be normal, and this could be a sign of an sexually transmitted infection.