Female pattern hair loss (androgenetic alopecia) is the most common type of permanent hair loss in women. It affects approximately 30 million women in the United States, according to the American Academy of Dermatology. It occurs in women of all races and ethnic groups, but is especially common among Caucasian women. Although the condition can develop as early as puberty, most women affected by the condition first experience hair loss around the time of menopause (end of menstruation). The rate of incidence tends to increase with age, affecting a majority of women aged 65 and older in varying degrees.

Hair plays a significant role in a woman’s self-image. The cultural and social importance placed on women’s hair and hair styling makes female pattern hair loss a debilitating condition for millions of women in the United States. Hair loss tends to have a greater psychological impact on women than on men.

Hair is composed of a protein called keratin and is produced in follicles located in the outer layer of the skin (epidermis). Each person is born with a pre-determined amount of follicles. The follicle holds the lower part of the hair shaft in place and contains blood vessels that stimulate new hair growth. The growth of hair from these follicles is cyclical and happens in three stages:

• Growth (anagen) phase. May last two to three years for any given hair. On a normal scalp, about 80 to 90 percent of hair follicles are in the growth phase at any given time.
  
  
• Involutional (catagen) phase. Reduction in size of the hair. Approximately 1 to 3 percent of hair on the scalp is undergoing involution at any given moment. The involutional phase is a transitional period the hair undergoes before being shed. Typically, it lasts about two or three weeks.
  
  
• Resting (telogen) phase. Shedding of hair from the scalp. Following involution, hairs go through a resting phase for about two to three months. At the end of this time, the hairs are shed and the growth cycle is reinitiated. On a normal scalp, approximately 5 to 10 percent of hairs on the scalp are in the resting phase at any given time, with about 75 hairs shed every day.
  
  

  

A full head of hair has about 100,000 hairs, with the exception of redheads, who have fewer hairs, and blondes, who have more. Up to 30 percent of hair may be lost by middle age as a normal part of the aging process.

Female pattern hair loss usually occurs around the time of menopause due to a combination of inherited factors, increased follicle sensitivity to the male sex hormone (androgen) dihydrotestosterone (DHT) and other systemic hormonal changes happening throughout the body. All of these factors combine to progressively shrink affected hair follicles around the hair part, decreasing the length of the growth phase and causing new hairs to be finer, thinner and to shed more rapidly. When the affected hair is shed, the root grows a new one that is finer and shorter. Over time, thick, colored terminal hairs become colorless vellus hairs (“peach fuzz”).

Female pattern hair loss is not the only cause of hair loss in women. For instance, hair loss can occur after pregnancy, due to the shift from an active growth phase during pregnancy to the usual pattern of growth, reduction and resting after childbirth. Hair loss may also result from physical or emotional stress or the discontinuation of birth control pills. Known as telogen effluvium, these forms of hair loss are characterized by an increased loss of hair over the entire scalp. Female pattern hair loss, on the other hand, is characterized by increased shedding of hair from only the top of the scalp. Telogen effluvium is usually a temporary condition, whereas female pattern hair loss is permanent.

Women experience hair loss nearly as frequently as men do. However, they tend not to lose as much hair due to hormonal differences and to have different balding patterns. Female pattern hair loss differs from male pattern hair loss in that women typically experience an overall thinning of the hair across the scalp as opposed to a “bald spot” or receding hairline. Women may also be able to disguise their hair loss more effectively than men because of differences in hair length and styling.