The presence of the necessary genes and hormones is not alone sufficient to cause baldness. Even after a person has reached puberty, susceptible hair follicles must continually be exposed to the hormone over a period of time for hair loss to occur. The age at which these effects finally manifest themselves varies from one individual to another and is related to a person’s genetic composition and to the levels of testosterone in the bloodstream.

There is another time factor that is poorly understood. Male hair loss does not occur all at once nor in a steady, straight-line progression. Hair loss is characteristically cyclical. People who are losing their hair experience alternating periods of slow and rapid hair loss and even stability. Many of the reasons that hair loss rates speed up and speed down are unknown, but we do know that with age, a person’s total hair volume will decrease.

Even when there is no predisposition to genetic balding, as a patient ages, some hairs randomly begin to miniaturize (shrink in length and width) in each follicular unit. As a result, each group will contain both of full terminal hairs and miniaturized hairs (similar to the very fine hairs that occur on the rest of the body and are clinically insignificant) making the area look less full. Eventually, the miniaturized hairs are lost, and the actual follicular units are reduced in number. In all adult patients, the entire scalp undergoes this aging process so that even the donor zone is not truly permanent, but will gradually thin, to some degree, over time. Fortunately, in most people, the donor zone retains enough permanent hair that hair transplantation is a viable male hair restoration procedure even for a patient well into his 70′s.