In the prenatal period, virilization refers to closure of the perineum, thinning and wrinkling of the scrotum, growth of the penis, 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.
High
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 male anatomy with no palpable testes. More often, the virilization is partial and the genitalia are ambiguous. It can also be associated with progestin-induced virilisation.
Low
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.
Normal virilization
In common as well as medical usage, virilization often refers to the process of normal male puberty. These effects include growth of the penis and testes, accelerated growth, development of pubic hair, and other androgenic hair of face, torso, and limbs, deepening of the voice, increased musculature, thickening of the jaw, prominence of the neck cartilage, and broadening of the shoulders.
Abnormal childhood virilization
Virilization can occur in childhood in both males and females due to excessive amounts of androgens. Typical effects of virilization in children are pubic hair, accelerated growth and bone maturation, increased muscle strength, acne, and adult body odor. In males, virilization may signal precocious puberty, while congenital adrenal hyperplasia and androgen producing tumors of the gonads or adrenals are occasional causes in both sexes.
In adolescent or adult females
Virilization in females can manifest as clitoral enlargement, increased muscle strength, acne, hirsutism, frontal hair thinning, deepening of the voice, and menstrual disruption due to anovulation. Some of the possible causes of virilization in females are:
Transgender people who were medically assigned female at birth sometimes elect to take hormone replacement therapy. This process causes virilization by inducing many of the effects of a typically male puberty. Many of these effects are permanent, but some effects can be reversed if the transgender individual stops or pauses their medical treatment.
Demasculinization refers to the reversal of virilization. Some but not all aspects of virilization are reversible. Demasculinization occurs naturally with andropause, pathologically with hypogonadism, and artificially or medically with antiandrogens, estrogens, and orchiectomy. It is desired by transgender women who have undergone the changes of pubertal masculinization, to restore & induce feminine physical traits that would otherwise be masked or never occur. Some virilized traits remain though, due to the fashion in which virilization affects a body's physiology.
Studies
Howell, W. M., Black, D. A., & Bortone, S. A.. . Copeia, 676–681.
