- This article is about smegma, a secretion of mammalian genitals. See Vernix caseosa for the substance that covers the skin of a baby at birth. See Smegma (band) for the experimental noise band.
Smegma, a transliteration of the Greek word σμήγμα for sebum, is a combination of exfoliated (shed) epithelial cells, transudated skin oils, and moisture, and can accumulate under the foreskin of males and within the vulva of females. It has a characteristic strong odor. Smegma is common to all mammals, male and female. Mycobacterium smegmatis is the characteristic bacterium involved in smegma production, and is generally thought to form smegma from epidermal secretions.
In healthy animals, smegma helps clean and lubricate the genitals. In veterinary medicine, analysis of this smegma is sometimes used for detection of urinary infections, such as trichomoniasis. Some have recommended periodic cleaning of male genitals to improve the health of the animal.
Both males and females produce smegma. In males smegma is produced and accumulates under the foreskin of uncircumcised individuals; in females it collects around the clitoris and in the folds of the labia minora.
Smegma is noticeable as a smooth or moist texture until it is allowed to accumulate, when it takes on its characteristic texture and appearance described in many texts as "cheesy". Because smegma tends to accumulate under the foreskin in males, its presence is less common and less noticeable in circumcised males.
The subpreputial moisture keeps the glans moist and may lubricate the movement of the foreskin. However, if allowed to accumulate and decay in the foreskin cavity it can provide an ideal medium for potentially pathogenic bacteria to colonize; current medical opinion is that allowing smegma to accumulate freely is unhealthy. Accumulation of smegma can cause or aggravate a variety of irritations known as balanitis.  Per the SEER database, the incidence of developing a primary penile cancer is less than 1 per 100,000 in the general population, but for uncircumcised males the rate is estimated to be as high as 1 per 600. Circumcision at a young age appears to be more protective against cancer of the penis than at the time of puberty or later. Early medical studies such as those by Plaut (1947) and Heins et al (1958) claimed that smegma accumulation led to the development of penile cancer, but the American Cancer Society states that more recent studies have failed to support this.Penile cancer is extremely uncommon in Jewish and Muslim populations that practice circumcision at infancy and between the ages of 3-13, respectively.  
Preventing accumulation is best done by rinsing the area with warm water. In females, the hood of the clitoris can be gently pulled back to wash away accumulated smegma. Some argue that soap is best avoided because it depletes natural skin oils and may cause non-specific dermatitis. Noticeably unpleasant cheese-like odors can be an indicator of a potentially serious medical problem, or a need to gently wash away excess with water. Deodorant sprays or washes may cause thrush or thrush-like conditions — washing using warm water only is recommended by health professionals for individuals with sensitive skin, or who suffer from dermatitis reactions to using soap-like products.
- ↑ http://www.horsecity.com/stories/090101/hea_beans_ML.shtml
- ↑ Ask Alice: Scent of an uncircumcised penis
- ↑ http://www.cirp.org/library/normal/wright1/
- ↑ 4.0 4.1 Risk Factors for Penile Cancer
- ↑ SEER Data
- ↑ http://www.circs.org/library/heins/
- ↑ Krieg R, Hoffman R. Current management of unusual genitourinary cancers. Part 1: Penile cancer. Oncology (Williston Park). 1999 Oct;13(10):1347-52.
- ↑ Daling JR, Madeleine MM, Johnson LG, Schwartz SM, Shera KA, Wurscher MA, Carter JJ, Porter PL, Galloway DA, McDougall JK, Krieger JN. Penile cancer: importance of circumcision, human papillomavirus and smoking in in situ and invasive disease. Int J Cancer. 2005 Sep 10;116(4):606-16.
- ↑ http://www.cirp.org/library/disease/balanitis/birley/
- O'Neill HJ, Gershbein LL. Lipids of human and equine smegma. Oncology 1976;33(4):161-6.
- Effects of hygiene among the uncircumcised Krueger H, Osborn L. J Fam Pract. 1986 Apr;22(4):353-5.
- The bacterial flora of preputial space Neubert U, Lentze I. Hautarzt. 1979 Mar;30(3):149-53.
- Wright J. How smegma serves the penis: Nature's assurance that the uncircumcised glans penis will function smoothly is provided by smegma. Sexology (New York) 1970;37(2):50-53.
- Parkash S, Jeyakumar K, Subramanya K, et al. Human subpreputial collection: its nature and formation. J Urol 1973;110(2):211-12.
- Van Howe RS, Hodges FM. The carcinogenicity of smegma: debunking a myth. J Eur Acad Dermatol Venereol 2006;20(9):1046.