The multiple causes include the side effects of drugs, associations with cancer, and possible links with eating disorders.

[1] Hirsutism is a type of hypertrichosis exclusive to women and children, resulting from an excess of androgen-sensitive hair growth.

It is linked to excessive male hormones in women, thus symptoms may include acne, deepening of the voice, irregular menstrual periods, and the formation of a more masculine body shape.

[23] This condition is also linked to metabolic disorders, such as anorexia, hormone imbalances, such as hyperthyroidism, or as a side effect of certain drugs.

The exact genetic mutation that causes congenital circumscribed, localized, and nevoid hypertrichosis is unknown.

[1] If the anagen phase increases beyond what is normal, that region of the body will experience excessive hair growth.

[7] Hypertrichosis is diagnosed clinically by the occurrence of hair in excess of what is expected for age, sex, and ethnicity in areas that are not androgen-sensitive.

[2] Depilation methods, such as trimming, shaving, and depilatories, remove hair to the level of the skin and produce results that last several hours to several days.

[25] Epilation methods, such as plucking, electrology, waxing, sugaring, threading remove the entire hair from the root, the results lasting several days to several weeks.

[needs update] One medicinal option suppresses testosterone by increasing the sex hormone-binding globulin.

[27] People with hair often found jobs as circus performers, making the best of their unusual appearance.

Fedor Jeftichew ("Jo-Jo the Dog-faced Man"), Stephan Bibrowski ("Lionel the Lion-faced Man"), Jesús "Chuy" Aceves ("Wolfman"), Annie Jones ("the bearded woman") and Alice Elizabeth Doherty ("The Minnesota Woolly Girl") all had hypertrichosis.

[8] Extensive hypertrichosis carries an emotional burden and can cause cosmetic embarrassment; however, some people attempt no treatments because they say it defines who they are.

[32] One record in history concerning congenital hypertrichosis lanuginosa is the hairy family of Burma, a four-generational pedigree of the condition.

[33] Julia Pastrana (1834–1860)[6] travelled throughout the United States in a freak show as the bearded lady, capturing the attention of many artists.

[6] She is portrayed as having dark extensive hairs distributed equally throughout the surface of her body, even on the palms of her hands.

On the contrary, hairy men and women with hypertrichosis are not necessarily isolated and they often live in courts as entertainers, together with other monster-like subjects.

[8] In summer 2019, at least 17 Spanish children have developed so-called “werewolf syndrome”, Spain's health ministry has said.

Instead of being treated with omeprazole, a drug that helps with gastric reflux, they had received a treatment of minoxidil, a medication against hair loss.

[40] In 1955, a female Müller's Bornean gibbon was obtained from Sarawak that exhibited abnormal hair growth in the facial region.

[41] Hypertrichosis (often mistakenly classified as hirsutism) is a well documented condition in horses with a hormonal disorder of the hypothalamus, called Cushing's disease.

It is the most common endocrine disease of the middle-aged to older horse, often resulting in fatal laminitis.