What is male pattern baldness?
Typically, at first the hair begins to thin (recede) at the sides (temples). At the same time, the hair usually becomes thin on the top of the head. A bald patch gradually develops in the middle of the scalp. The receding sides and the bald patch on the top (the crown) gradually enlarge and join together, leaving a patch at the front. The patch at the front eventually thins as well.
A rim of hair is often left around the back and sides of the scalp. In some men, this rim of hair also thins and goes to leave a completely bald scalp.
Who gets male pattern baldness?
Male hormones are involved in causing these changes. The level of the main male hormone, testosterone, is normal in men with baldness. Hair follicles convert testosterone into another hormone called dihydrotestosterone. For reasons that are not clear, affected hair follicles become more sensitive to dihydrotestosterone, which causes the hair follicles to shrink. It is also not clear why different hair follicles are affected at different times to make the balding process gradual.
The condition is hereditary (genetic); the location of the gene was identified in 2008. It is also not clear why only scalp hairs are affected and not other areas such as the beard or armpits.