When the growth phase ends, the hair follicle enters the resting phase of its cycle. This lasts for a few months only. Club hair is the old hair that stops growing and simply remains in the follicle until a new hair forms underneath and pushes it out. We lose club hair all the time without noticing it - between 20 and 100 each day. Fortunately the growth or resting phases are not synchronised in adjacent follicles.
Hair growth is under hormonal control.
The hormones govern the development of hair that appears after puberty. The male hormone, testosterone, governs beard, body hair and hair in the armpits. The female hormone, oestrogen, generally prevents hair growth on the chin and encourages it to grow on the head. Occasionally women develop signs of male patterned baldness at menopause when oestrogen levels drop. Treatment with oestrogen has been successful in restoring hair growth.