Baldness is determined by multiple genetic factors. It cannot be categorically stated that baldness follows the mother's line or anyone else's, or that it skips generations.

Both men and women lose hair density as they age. Men develop a typical pattern of baldness, associated with the presence of the male hormone testosterone. Men who do not produce testosterone (because of genetic abnormalities or castration) do not develop this pattern of baldness. The use of steroids during adolescence and young adulthood may accelerate the effects of testosterone on baldness. Women also develop a characteristic pattern of hair loss. See male-pattern baldness; female-pattern baldness.

Occurring most often on the scalp, alopecia usually develops gradually and may be all over (diffuse) or patchy.

Usually baldness is not caused by a disease but is genetic and permanent. Inherited or "pattern baldness" affects many more men than women. About 25% of men begin to bald by the time they are 30 years old, and about two-thirds are either bald or have a balding pattern by age 60.

On average, about 100 hairs are lost from the head every day. The average scalp contains about 100,000 hairs (blondes 140,000, brunettes 155,000 and redheads only 85,000).

Each individual hair survives for an average of 4.5 years, during which time it grows about half an inch a month. Usually in its 5th year, the hair falls out and is replaced within 6 months by a new one. Genetic baldness is caused by the body's failure to produce new hairs and not by excessive hair loss.