Male pattern baldness refers to a loss of hair on the scalp in men. It happens as hormone levels change over a man’s lifetime, and especially in the later years. This process can begin at any age. About two thirds of men are either bald or have a balding pattern by the age of 60. The Norwood Scale is the leading classification system used to measure the extent of male pattern baldness. Men typically lose their hair in one of several common patterns over the course of many decades.