Biology
The beard develops during puberty. Beard growth is linked to stimulation of hair follicles in the area by dihydrotestosterone, which continues to affect beard growth after puberty. Hair follicles from different areas vary in what hormones they are stimulated or inhibited by; dihydrotestostorone also promotes balding. Dihydrotestosterone is produced from testosterone, the levels of which vary with season; thus beards grow faster in summer.
Difficulties in measuring beard growth have led to controversies concerning the effects of hormonal activity on short term pogonotrophy. For example, a physicist had to spend periods of several weeks on a remote island in comparative isolation. He noticed that his beard growth diminished, but the day before he was due to leave the island it increased again, to reach unusually high rates during the first day or two on the mainland. He studied the effect and concluded that the stimulus for increased beard growth was related to the resumption of sexual activity. However, at that time professional pogonologists reacted vigorously and almost dismissively.
How fast the beard grows is also genetic.
Read more about this topic: Beard
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