Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This in ...

s. Virilization is most commonly used in three medical and biology of sex contexts: prenatal biological sexual differentiation, the postnatal changes of typical chromosomal male (46, XY)

puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a ...

, and excessive androgen effects in typical chromosomal females (46, XX). It is also the intended result of

androgen replacement therapy Androgen replacement therapy (ART), often referred to as testosterone replacement therapy (TRT) or hormone replacement therapy (HRT), is a form of hormone therapy in which androgens, often testosterone, are supplemented or replaced exogenously ...

in males with

delayed puberty Delayed puberty is when a person lacks or has incomplete development of specific sexual characteristics past the usual age of onset of puberty. The person may have no physical or hormonal signs that puberty has begun. In the United States, girls ...

and

low testosterone Hypogonadism means diminished functional activity of the gonads—the testes or the ovaries—that may result in diminished production of sex hormones. Low androgen (e.g., testosterone) levels are referred to as hypoandrogenism and low estrogen ...

Prenatal virilization

In the prenatal period, virilization refers to closure of the perineum, thinning and wrinkling (rugation) of the

scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...

, growth of the penis, and closure of the urethral groove to the tip of the

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

. In this context, ''masculinization'' is synonymous with ''virilization.'' Prenatal virilization of genetic females and undervirilization of genetic males are common causes of

ambiguous genitalia Intersex people are individuals born with any of several sex characteristics including chromosome patterns, gonads, or genitals that, according to the Office of the United Nations High Commissioner for Human Rights, "do not fit typical ...

and

intersex Intersex people are individuals born with any of several sex characteristics including chromosome patterns, gonads, or genitals that, according to the Office of the United Nations High Commissioner for Human Rights, "do not fit typical b ...

conditions.

High

Prenatal virilization of a genetically female fetus can occur when an excessive amount of androgen is produced by the fetal

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex ...

s or is present in maternal blood. In the severest form of

congenital adrenal hyperplasia Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders characterized by impaired cortisol synthesis. It results from the deficiency of one of the five enzymes required for the synthesis of cortisol in the adrenal cortex ...

, complete masculinization of a genetically female fetus results in an apparently normal male anatomy with no palpable

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

. More often, the virilization is partial and the genitalia are ambiguous. It can also be associated with

progestin-induced virilisation Maternal use of androgens or high doses of certain weakly androgenic synthetic progestogens (progestins) structurally related to testosterone can masculinize (virilize) the external genitalia of a female fetus during susceptible times in pregna ...

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

Normal virilization

In common as well as medical usage, virilization often refers to the process of normal male

. 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 Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bon ...

, accelerated growth and bone maturation, increased muscle strength,

acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...

, and adult body odor. In males, virilization may signal

precocious puberty In medicine, precocious puberty is puberty occurring at an unusually early age. In most cases, the process is normal in every aspect except the unusually early age and simply represents a variation of normal development. In a minority of childr ...

, while

and androgen producing tumors (usually) of the

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...

s 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,

menstrual The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs a ...

disruption due to anovulation, and a strengthened libido. Some of the possible causes of virilization in females are: *

Androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This in ...

-producing tumors of the **

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

s (see adrenal tumor) **

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The h ...

(see

pituitary adenoma Pituitary adenomas are tumors that occur in the pituitary gland. Most pituitary tumors are benign, approximately 35% are invasive and just 0.1% to 0.2% are carcinomas.Hyperthecosis *

Hypothyroidism Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as ...

Anabolic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone as well as synthetic androgens that are structurally related and have similar effects ...

exposure * Congenital adrenal hyperplasia due to 21-hydroxylase deficiency (late-onset) * Conn's syndrome

Medically induced virilization in transgender people

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.

Permanent virilization effects

* Deepening of the voice * Growth of facial and body hair * Male-pattern

baldness Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarr ...

* Enlargement of the

clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the op ...

Breast atrophy Breast atrophy is the normal or spontaneous atrophy or shrinkage of the breasts. Breast atrophy commonly occurs in women during menopause when estrogen levels decrease. It can also be caused by hypoestrogenism and/or hyperandrogenism in women in ...

– possible shrinking and/or softening of breasts

Reversible virilization effects

* Further muscle development (especially upper body) * Increased sweat and changes in body odor * Prominence of veins and coarser skin * Alterations in blood lipids (

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...

and triglycerides) * Increased red blood cell count

Demasculinization

Demasculinization refers to the reversal of virilization. Some but not all aspects of virilization are reversible. Demasculinization occurs naturally with andropause, pathologically with

hypogonadism Hypogonadism means diminished functional activity of the gonads—the testes or the ovaries—that may result in diminished production of sex hormones. Low androgen (e.g., testosterone) levels are referred to as hypoandrogenism and low estroge ...

, and artificially or medically with antiandrogens,

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

s, and orchiectomy. It is desired by

transgender women A trans woman or a transgender woman is a woman who was assigned male at birth. Trans women have a female gender identity, may experience gender dysphoria, and may transition; this process commonly includes hormone replacement therapy and so ...

who have undergone the changes of pubertal masculinization, to restore and induce feminine physical traits that would otherwise be masked or never occur. Some virilized traits remain though (such as body hair, a hard jawline and an enlarged

larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...

), due to the fashion in which virilization affects a body's physiology.

References

External links

{{Reproductive physiology Sexual dimorphism Metabolism Physiology Testosterone