Hair goes through three phases: an anagen phase when the hair is growing, a catagen phase when the hair stops growing, and finally a telogen phase where it is resting before it begins to grow again. Some scientists have suggested that nasal hair becomes more prominent as men age because of the influence of testosterone on the length of the anagen (growing) phase.
In men, during puberty, as testosterone levels increase, small hairs on the face, underarms, chest, legs, arms and pubic area turn into large hairs that remain in anagen for longer periods. To the annoyance of most men, later in life, the follicles in the nose and ear become sensitive to testosterone and also increase in size, resulting in larger hairs. Paradoxically, scalp hair follicles of genetically predisposed men respond in the opposite way: they spend less time in the anagen phase, which leads to baldness.
However, the exact mechanism is still not well understood – more research has been done on why men lose their hair, rather than the problem of having too much.
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