Hirsutism is a condition seen in women that is associated with development of androgen-dependent terminal hair (coarse, pigmented) following a male-pattern distribution (face, chest, abdomen, back).
Hair in different areas of the body demonstrates varying levels of androgen sensitivity, depending mostly on local sensitivity of androgen receptors and 5-alpha-reductase activity levels. Terminal hair, also known as sexual hair, is dependent on androgens for development and maintenance.  Hair response to androgens varies from person to person and includes increase in follicle size, fibre diameter, and the amount of time spent in anagen (the growth-cycle phase).  
Around 70% to 80% of women with androgen excess manifest hirsutism.  Excessive sexual hair may be accompanied by signs of virilisation: male-pattern alopecia, deepening of the voice, clitoromegaly, increased muscle bulk. When present, virilisation indicates an underlying condition associated with moderately to severely elevated androgen levels.
The extent of terminal hair varies by ethnic background and the method used to evaluate it.  Women of Asian background have less body hair, as compared with southern European women. Among American women (white and black), the prevalence of hirsutism, as assessed by a standard score, is 20%. 
Professor of Medicine
Weill Cornell Medical College Qatar
SLA declares that he has no competing interests.
Senior Lecturer/Honorary Consultant Physician
Academic Endocrinology, Diabetes and Metabolism
Hull York Medical School
Michael White Diabetes Centre
Hull Royal Infirmary
TS declares that he has no competing interests.
Dr Stephen L. Atkin and Dr Thozhukat Sathyapalan would like to gratefully acknowledge Dr Shehzad Basaria and Dr Milena Braga-Basaria, the previous contributors to this monograph. SB and MBB declare that they have no competing interests.
Professor of Investigative Endocrinology
JM declares that he has no competing interests.
Department of Internal Medicine
VA Medical Center
University of Iowa
UK declares that he has no competing interests.
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