Masculinization

Virilization or masculinization is the biological development of sex differences, changes that make a male body different from a female body. Most of the changes of virilization are produced by androgens. Virilization is most commonly used in three medical and biology of gender contexts: prenatal sexual differentiation, the postnatal changes of normal male puberty, and excessive androgen effects in girls or women.

In the prenatal period, virilization refers to closure of the perineum, thinning and wrinkling (rugation) of the scrotum, growth of the phallus, and closure of the urethral groove to the tip of the penis. In this context, masculinization is synonymous with virilization.

Prenatal virilization of genetic females and undervirilization of genetic males are common causes of ambiguous genitalia and intersex conditions.

Prenatal virilization of a genetically female fetus can occur when an excessive amount of androgen is produced by the fetal adrenal glands or is present in maternal blood. In the severest form of congenital adrenal hyperplasia, complete masculinization of a genetically female fetus results in an apparently normal baby boy with no palpable testes. More often, the virilization is partial and the genitalia are ambiguous.

It can also be associated with progestin-induced virilisation.

Undervirilization can occur if a genetic male cannot produce enough androgen or the body tissues cannot respond to it. Extreme undervirilization occurs when no significant androgen hormones can be produced or the body is completely insensitive to androgens. Both result in a female body. Partial undervirilization produces ambiguous genitalia part-way between male and female. The mildest degree of undervirilization may be a slightly small penis. Examples of undervirilization are androgen insensitivity syndrome, 5 alpha reductase deficiency, and some forms of congenital adrenal hyperplasia.

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