Genetic - Male Pattern Balness
Aging encourages hair loss affecting approximately 50% males / 20% females, tending to follow a typical receding pattern. Genetic pattern hair loss aside from other hair diseases starts from the top advancing down the head.
One of the causes of losing hair is the male hormone dihydrotestosterone (DHT). Testosterone converted in the body as DHT by the enzyme 5 alpha reductase, causes the growth of follicles to cease in people prone to their genetic make-up. This targets the crown and mid scalp areas. Frontal hair loss has other causes currently under research.
The Norwood Hair Loss Classification Scale is a way to measure the extent of male pattern hair loss an individual is experiencing at a given time, and is the generally accepted standard when describing hair loss in general. The classification scale was originated with Dr James Hamilton in the 1950s who developed the baldness classification system, which was later revised by Dr O'Tar Norwood in the 1970’s by modifying the stages and adding 3a, 3 vertex, 4a and 5a. Men typically lose hair in several patterns. The most common are receding at the temples, on the top back of the head known as vertex, and diffuse thinning where hair over large areas begins to thin, without a specific change to the hairline. Combinations of these types of losses also occur.