Female pattern hair loss is the most common type of hair loss in women. The condition is genetically predetermined, though factors such as age and androgen (male sex hormones) levels are commonly associated with the timing of its onset and how far it progresses. It most often begins during menopause (end of menstruation) but may begin as soon as puberty in very rare cases.

Dihydrotestosterone (DHT) and an enzyme (a complex protein found in body cells) known as 5-alpha reductase are involved in the androgenic alopecia process. Women with large amounts of this enzyme produce excess amounts of DHT, the hormone primarily responsible for hair loss. This subsequently reduces levels of estrogen, a hormone that naturally counteracts the affects of DHT. Over time, this excess DHT causes the hair follicle to shrink or even stops hair growth.

Women who experience hair loss early in life typically have a family history of androgenetic alopecia on both sides of the family, though this occurs rarely. Female pattern hair loss that begins around the time of menopause generally occurs due to a combination of heredity, an increased sensitivity to androgens and other hormonal changes occurring normally throughout the body.

Unusually high androgen levels can also cause hair loss to occur and may be confused with female pattern hair loss in some patients.  An androgen imbalance may be present if hair loss occurs around the temples (more of a male pattern) or in conjunction with any of the following conditions:

• Menstrual disorders (e.g., abnormal uterine bleeding)
  
  
• Acne
  
  
• Galactorrhea (discharge of milk from the nipples without pregnancy or childbirth)
  
  
• Infertility
  
  
• Abnormal development of male characteristics (e.g., low voice, hirsutism [excess hair in areas where hair growth usually does not appear in females], increased muscle mass)