Androgenetic alopecia is a common form of hair loss in both men and women. In men, it is also known as male pattern baldness, and in women, it is also known as female pattern hair loss.

In men, hair is lost in a well-defined pattern, beginning above both temples. Over time, the hairline moves back (recedes) to form a characteristic "M" shape. Hair also thins at the top of the head (vertex or crown), often progressing to partial or complete baldness.

The pattern of hair loss in women differs from male-pattern baldness. In women, the hair becomes thinner at the top of the head, and the middle part widens. The hairline does not typically recede.  Androgenetic alopecia in women rarely leads to total baldness.

Androgenetic alopecia in men has been associated with several other medical conditions, including coronary heart disease and enlargement of the prostate. Additionally, prostate cancer, disorders of insulin resistance (such as diabetes and obesity), and high blood pressure (hypertension) have been related to androgenetic alopecia. 

In women, this form of hair loss is associated with an increased risk of polycystic ovary syndrome (PCOS). PCOS is characterized by a hormonal imbalance that can lead to irregular menstruation, acne, excess hair elsewhere on the body (hirsutism), and weight gain.

Androgenetic alopecia affects an estimated 50 million men and 30 million women in the United States. Androgenetic alopecia can start as early as a person's teens, and the risk increases with age; more than 50 percent of men over age 50 have some degree of hair loss. In women, hair loss is most likely after menopause.

A variety of genetic and environmental factors likely play a role in causing androgenetic alopecia. Although researchers are studying risk factors that may contribute to this condition, most of these factors remain unknown. Researchers have determined that this form of hair loss, particularly in men, is related to hormones called androgens, specifically an androgen called dihydrotestosterone (DHT). Androgens play a role in female pattern hair loss, but other factors that are not yet known are also involved. 

Androgens are important for normal male sexual development before birth and during puberty. Androgens also have other important functions in both males and females, such as regulating hair growth and sex drive. 

Hair growth begins under the skin in structures called follicles. Each strand of hair normally grows for 2 to 6 years, goes into a resting phase for several months, and then falls out. The cycle starts over when the follicle begins growing a new hair. 

Androgens help control this cycle. However, too much stimulation of hair follicles by androgens may lead to a shorter growth period, resulting in shorter and thinner strands of hair. The growth of new hair to replace strands that are shed is also delayed. Together, these changes lead to  hair thinning or loss.

Researchers suspect that variants (also called mutations) in several genes play a role in androgenetic alopecia. However, scientific studies have confirmed only that variations in one gene, the AR gene, are involved in this condition. The AR gene provides instructions for making a protein called an androgen receptor. Androgen receptors allow the body to respond appropriately to DHT and other androgens. Studies suggest that variations in the AR gene result in androgen receptors that are more easily stimulated by androgens than normal, leading to increased activity of the receptors in hair follicles. It remains unclear, however, how these genetic changes increase the risk of hair loss in men and women with androgenetic alopecia.

Researchers continue to investigate the connection between androgenetic alopecia and other medical conditions, such as coronary heart disease and prostate cancer in men and polycystic ovary syndrome in women. They believe that some of these disorders may be associated with elevated androgen levels, which may help explain why they tend to occur with androgen-related hair loss.

Genetic and Rare Diseases Information Center

• Androgenetic alopecia

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• ALOPECIA, ANDROGENETIC, 1; AGA1
• ALOPECIA, ANDROGENETIC, 2; AGA2
• ALOPECIA, ANDROGENETIC, 3; AGA3

Scientific Articles on PubMed

• PubMed

• Amoretti A, Laydner H, Bergfeld W. Androgenetic alopecia and risk of prostate cancer: a systematic review and meta-analysis. J Am Acad Dermatol. 2013 Jun;68(6):937-43. doi: 10.1016/j.jaad.2012.11.034. Epub 2013 Feb 8. Citation on PubMed
• Cousen P, Messenger A. Female pattern hair loss in complete androgen insensitivity syndrome. Br J Dermatol. 2010 May;162(5):1135-7. doi: 10.1111/j.1365-2133.2010.09661.x. Epub 2010 Feb 1. Citation on PubMed
• Hillmer AM, Hanneken S, Ritzmann S, Becker T, Freudenberg J, Brockschmidt FF, Flaquer A, Freudenberg-Hua Y, Jamra RA, Metzen C, Heyn U, Schweiger N, Betz RC, Blaumeiser B, Hampe J, Schreiber S, Schulze TG, Hennies HC, Schumacher J, Propping P, Ruzicka T, Cichon S, Wienker TF, Kruse R, Nothen MM. Genetic variation in the human androgen receptor gene is the major determinant of common early-onset androgenetic alopecia. Am J Hum Genet. 2005 Jul;77(1):140-8. doi: 10.1086/431425. Epub 2005 May 18. Citation on PubMed or Free article on PubMed Central
• Levy-Nissenbaum E, Bar-Natan M, Frydman M, Pras E. Confirmation of the association between male pattern baldness and the androgen receptor gene. Eur J Dermatol. 2005 Sep-Oct;15(5):339-40. Citation on PubMed
• Quinn M, Shinkai K, Pasch L, Kuzmich L, Cedars M, Huddleston H. Prevalence of androgenic alopecia in patients with polycystic ovary syndrome and characterization of associated clinical and biochemical features. Fertil Steril. 2014 Apr;101(4):1129-34. doi: 10.1016/j.fertnstert.2014.01.003. Epub 2014 Feb 15. Citation on PubMed
• Schweiger ES, Boychenko O, Bernstein RM. Update on the pathogenesis, genetics and medical treatment of patterned hair loss. J Drugs Dermatol. 2010 Nov;9(11):1412-9. Citation on PubMed
• Yazdan P. Update on the genetics of androgenetic alopecia, female pattern hair loss, and alopecia areata: implications for molecular diagnostic testing. Semin Cutan Med Surg. 2012 Dec;31(4):258-66. doi: 10.1016/j.sder.2012.08.003. Citation on PubMed
• Zhuo FL, Xu W, Wang L, Wu Y, Xu ZL, Zhao JY. Androgen receptor gene polymorphisms and risk for androgenetic alopecia: a meta-analysis. Clin Exp Dermatol. 2012 Mar;37(2):104-11. doi: 10.1111/j.1365-2230.2011.04186.x. Epub 2011 Oct 10. Citation on PubMed