Based on an excess of testosterone, which begins during puberty, hair may fall out prematurely. As a result, many men notice hereditary hair loss early on. The hair root is hypersensitive to the hormone dihydrotestosterone (DHT). It weakens the hair roots and prematurely renders them inactive. This shortens their growth phases and terminates their life prematurely. If more and more hair roots die in this manner, baldness will ensue.