Male pattern baldness is most often caused by an excess of testosterone - the male hormone - produced in their bodies. the condition is usually hereditary. Because testosterone is a male hormone, the myth has arisen that bald men are more virile - and myth it is (I'm sad to say!) Occasional hair loss can occur as a result of stress, or a change in hormone levels, and this can affect women, sometimes after childbirth, but it is usually temporary, and responds to treatment. the other cause is alopecia - the inability of the body to grow hair anywhere - the most famous sufferer of this condition is Duncan Goodhew, former swimmer.