Hirsutism pathophysiology

Hirsutism Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Hirsutism from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Criteria

History and Symptoms

Physical Examination

Laboratory Findings

MRI

Echocardiography or Ultrasonography

Treatment

Medical Therapy

Pharmacological therapy

Non-pharmacological therapy

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Hirsutism pathophysiology On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Hirsutism pathophysiology

CDC on Hirsutism pathophysiology

Hirsutism pathophysiology in the news

Blogs on Hirsutism pathophysiology

Directions to Hospitals Treating Hirsutism pathophysiology

Risk calculators and risk factors for Hirsutism pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: ; Ogheneochuko Ajari, MB.BS, MS [2] Rasam Hajiannasab M.D.[3]

## Overview[edit | edit source]

The growth of hair on sex-specific areas of the body occurs due to androgens. Androgens induce vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and more heavily pigmented.

## Pathophysiology[edit | edit source]

The growth of hair on sex-specific areas of the body occurs due to androgens. Androgens stimulate the growth of vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and have increased pigmentation (darker).[1][2][3][4]

### Types of hair[edit | edit source]

* There are approximately 5 million hair follicles at birth in humans with about 80,000 to 150,000 of them on the scalp.
* The quality of hair is determined by hormones and other intrinsic characteristics of the hair follicle.
* There are various types of hair which include:
* Lanugo hair: The soft hair which covers the fetal skin and it disappears within the first three months after the fetus delivery.
* Vellus hair: This is fine, soft hair that is not pigmented. It covers most of the body before the pubertal period.
* Terminal hair: This is long, coarse and pigmented. Pubertal androgens for example dihydrotestosterone (DHT) convert vellus hair to terminal hair.

### Phases of Hair Growth Cycle[edit | edit source]

* There are 3 phases of hair growth cycle:
* The hair growth phase (termed Anagen phase): This phase varies, depending on the body area affected. It is approximately 4 months for facial hair.
* The involutional phase (Catagen phase): This phase is approximately 2-3 weeks.
* The resting phase (Telogen phase): The hair shaft separates from the dermal papillae at the base of the follicle, which terminates growth.

### Pathogenesis[edit | edit source]

* The growth of sexual hair is dependent on the presence of androgens.
* Androgens induce vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and more heavily pigmented.
* Hirsutism is caused by increased androgen production and/or an increased sensitivity of the hair follicles to androgens.
* Hyperandrogenism, resulting from any factors, prolongs the anagen(growth) phase of androgen-sensitive hairs, resulting in their conversion from fine, light, vellus hairs to coarse, dark, terminal hairs.
* The response of hair follicle to androgens and other factors such as local 5 alpha-reductase activity determines the level of conversion of hair from the vellus type to terminal hair.[1]

Hair Follicle[5]
Courtesy to WikiMedia

* Growth recommences with the formation of new hair shaft by the reactivation of the dermal papillae, thereby replacing the old hair.
* The hair growth cycle takes months to years to be completed, causing a delay in hair growth response to changes from effects of androgens.
* DHT is a hormone that acts on the hair follicle to produce terminal hair.
* Differences in the activity of DHT explains why women with the same plasma level testosterone, have different degrees of hirsutism.
* It is speculated that insulin, at high enough concentration, stimulates the ovarian theca cells to produce androgens.
* There may also be an effect of high levels of insulin to activate the insulin-like growth factor-I (IGF-1) receptor in those same cells resulting in increased androgen production.

## Associated Conditions[edit | edit source]

Common conditions associated with hirsutism include:

* Diabetes (in PCOS )
* Acne
* Fertility problems

## References[edit | edit source]

1. ↑ 1.0 1.1 Deplewski D, Rosenfield RL (2000). "Role of hormones in pilosebaceous unit development". Endocr. Rev. 21 (4): 363–92. doi:10.1210/edrv.21.4.0404. PMID 10950157.
2. ↑ Messenger AG (1993). "The control of hair growth: an overview". J. Invest. Dermatol. 101 (1 Suppl): 4S–9S. PMID 8326154.
3. ↑ Hatch R, Rosenfield RL, Kim MH, Tredway D (1981). "Hirsutism: implications, etiology, and management". Am. J. Obstet. Gynecol. 140 (7): 815–30. PMID 7258262.
4. ↑ Labrie F (1991). "Intracrinology". Mol. Cell. Endocrinol. 78 (3): C113–8. PMID 1838082.
5. ↑ "Category:Hair follicle - Wikimedia Commons".

Template:WH Template:WS