Under normal conditions, scalp hairs live for about three years (the anagen, or growing, phase); they then enter the telogen, or resting, phase. During the three-month telogen period, the hair root shrivels up into a small white "club," then the hair falls out. It is therefore normal to lose about 100 hairs every day, more of them on days when shampooing loosens the hairs that are ready to fall out. The hairs are then replaced by the body.
Sometimes people worried about losing their hair start noticing hairs on their pillow or in the sink, not realizing that they've always been there. A close look at these will usually reveal the white club at the end, showing that these hairs were already dead. Normally, about 10% of scalp hairs are in the telogen phase.
There are several circumstances that produce a "shock to the system" that alters the hair growth rhythm. As a result, as much as 30%-40% of the hairs can cycle into telogen. Three months later, hairs come out in a massive shedding (effluvium), especially near the front of the scalp.
