How does androgen excess affect hair growth?

Updated: Mar 14, 2018
  • Author: Mohamed Yahya Abdel-Rahman, MD, MSc; Chief Editor: Richard Scott Lucidi, MD, FACOG  more...
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Answer

Androgen excess affects mainly the pilosebaceous unit (PSU) and the reproductive system. The PSU secretes sebum and is the unit from which hair grows. Three types of hair, lanugo, vellus, and terminal hairs, exist. The fine hairs of the fetus are lanugo and the peach fuzz hair of adults is vellus hair. These hairs are fine, short, and nonpigmented. Thick and pigmented hair is referred to as terminal hair. Those hairs of the pubic, axillary, sternal, and facial areas are responsive to androgens and those in scalp, eyelashes, and eyebrows are androgen-independent. Their prevalence depends largely on genetics. As androgen levels rise, more vellus hairs in the androgen-sensitive areas are converted into terminal hairs, resulting in hirsutism.

Androgens prolong the growth phase of hair and promote their conversion from vellus to terminal type. Hirsutism affects 70-80% of women with androgen excess. Sebum production from the PSU is also increased by androgens. [21]


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