Individual levels of sensitivity to testosterone production determine the amount of hair growth on each human body. As a girl enters puberty, her body's hair follicles become more sensitive to the male hormone testosterone, which the female body produces in small amounts. Consequently, her fine hair may grow dark and coarse in certain areas. Abnormal amounts of body hair may be caused by anorexia, polycystic ovarian disease or cysts.
As an indication, the market for male shaving lotions and soap in the UK in 1986 was £114.3 million. That for female shaving lotions and depilatories was £17.9 million. According to a 1992 UK study, an estimated 25% of young women have noticeable facial hair, 15% have noticeable lower back hair and 15% have noticeable chest hair.