What Is It, Causes, Signs and Symptoms, and More

Author:Maria Emfietzoglou, MD

Editors:Alyssa Haag,Emily Miao, PharmD,Kelsey LaFayette, DNP, ARNP, FNP-C

Illustrator:Jessica Reynolds, MS

Copyeditor:David G. Walker

What is hypertrichosis?

Hypertrichosis, also known as werewolf syndrome, is a rare condition characterized by excessive hair growth that may develop all over the body or be isolated to specific areas. Hypertrichosis may be congenital (i.e., present at birth) or acquired (i.e., arising later in life). Acquired hypertrichosis can further be classified as generalized or localized to small patches. 

Individual with excessive hair growth over entire body.

What is the difference between hypertrichosis and hirsutism?

Hypertrichosis is a condition independent of androgen production, whereas hirsutism results in excess hair growth in androgen-dependent areas of the body, such as the chin, upper lip, chest, and back. Hirsutism specifically occurs in those assigned females at birth. 

Excited Mo character in scrubs
Join millions of students and clinicians who learn by Osmosis!
Start Your Free Trial

What causes hypertrichosis?

Congenital hypertrichosis can either be inherited or result from a spontaneous mutation. There are various forms of congenital hypertrichosis, including congenital hypertrichosis lanuginosa, which is characterized by excessive growth of an unpigmented, soft, and fine hair called lanugo hair. Congenital hypertrichosis terminalis is also another type of congenital hypertrichosis and is characterized by the excess growth of fully pigmented terminal hair (i.e., long and thick hair) that covers most of the body as well as by the presence of gingival hyperplasia (i.e., increase in size of the gingiva, or gums). Another form of congenital hypertrichosis is naevoid hypertrichosis where excessive growth of terminal hair is localized to a circumscribed area (e.g., an eyebrow) or may be localized to a birthmark (e.g., a congenital melanocytic nevus, or mole). 

On the other hand, acquired hypertrichosis may be associated with a variety of conditions. For instance, generalized acquired hypertrichosis may be associated with malnutrition, anorexia nervosa, hypothyroidism, malignancy, medications (e.g., cyclosporine, phenytoin), and porphyria cutanea tarda (i.e., a rare disorder characterized by photosensitivity; painful, blistering skin lesions; and tea-coloured urine). Localized acquired hypertrichosis may occur in areas where there has been repetitive rubbing or scratching, a previous application of plaster casts, or where there is topical administration of medications (e.g., minoxidil, steroids).

What are the signs and symptoms of hypertrichosis?

Signs and symptoms of hypertrichosis can vary depending on the cause. Excessive hair growth may present at birth or occur later in life and can also be generalized or localized to specific areas. Additionally, the type of body hair can vary based on the different forms of hypertrichosis and can be vellus hair (i.e., pigmented or nonpigmented, short hair), lanugo hair, or terminal hair. Gingival hyperplasia may also be present. 

How is hypertrichosis diagnosed?

Diagnosis of hypertrichosis is based on the individual’s history and clinical presentation. Based on the site of hair growth on exam, hirsutism may be able to be ruled out. Family history may also be helpful in identifying an inherited, congenital disorder, while an individual’s history of other medical conditions or use of medications can help identify an acquired cause. 

How is hypertrichosis treated?

Since there is no cure for hypertrichosis, treatment focuses on hair removal, which is typically done regularly as the hair continues to grow back. There are various methods for hair removal with short-term results, such as shaving, waxing, and chemical epilation (i.e., use of cosmetic creams to remove hair). Methods with long-term results include laser and electrolysis in which a small fine needle is inserted into the hair follicles and small electrical charges destroy the follicles. Avoidance of medications that have been associated with hypertrichosis (e.g., minoxidil) may also be advised. 

What are the most important facts to know about hypertrichosis?

Hypertrichosis is a condition characterized by excessive hair growth that, in contrast to hirsutism, is independent of androgen levels. Hypertrichosis can be either congenital, such as congenital hypertrichosis lanuginosa, congenital hypertrichosis terminalis, and naevoid hypertrichosis; or acquired due to malnutrition, malignancy, exposure to medications, and repetitive scratching, among other causes. The type of hair can be vellus, lanugo, or terminal depending on the form of hypertrichosis. Diagnosis is based on presentation and history, while treatment focuses on hair removal using a variety of methods that can have short-term or more long-term results.

Quiz yourself on Hypertrichosis

7 Questions available

Quiz now!

Watch related videos:

Mo with coat and stethoscope

Want to Join Osmosis?

Join millions of students and clinicians who learn by Osmosis!

Start Your Free Trial

Related links

Androgens and antiandrogens
Hair, skin and nails
Virilization: Clinical practice

Resources for research and reference

Hernandez MI, Castro A, Bacallao K, et al. Hormonal profile and androgen receptor study in prepubertal girls with hypertrichosis. Int J Pediatr Endocrinol. 2014;2014(1):6. doi:10.1186/1687-9856-2014-6

Kaler SG, Patrinos ME, Lambert GH, Myers TF, Karlman R, Anderson CL. Hypertrichosis and congenital anomalies associated with maternal use of minoxidil. Pediatrics. 1987;79(3):434-436.

Mathieu M, Goldfarb A, Berquin P, Boudailliez B, Labeille B, Piussan C. Trichomegaly, pigmentary degeneration of the retina and growth disturbances: a probable autosomal recessive disorder. Genet Couns. 1991;2(2):115-118.

Nistico SP, Del Duca E, Farnetani F, et al. Removal of unwanted hair: efficacy, tolerability, and safety of long-pulsed 755-nm alexandrite laser equipped with a sapphire handpiece. Lasers Med Sci. 2018;33(7):1479-1483. doi:10.1007/s10103-018-2503-z

Rossi A. Alopecia areata and hypertrichosis: a case report. Prevention & Research. Published online 2012. doi:

‌Salido R, Gómez-García FJ, Garnacho-Saucedo G, Galán-Gutiérrez M. Acquired generalized hypertrichosis due to diazoxide. Actas Dermosifiliogr. 2013;104(2):166-167. doi:10.1016/

Shah IH, Zeerak S, Sajad P, Bashir S, Bhat YJ, Mubashir S. Congenital hypertrichosis lanuginosa. Indian J Dermatol Venereol Leprol. 2018;84(2):248. doi:10.4103/ijdvl.IJDVL_525_16

Tančić-Gajić M, Vujović S, Dujmović I, et al. Acquired hypertrichosis lanuginosa: typical presentation and unusual association. Arch Iran Med. 2015;18(7):450-452.