Each strand of hair grows from a hair follicle and each hair follicle has its own life cycle. This means that each strand of hair grows independently of the surrounding strands. If all of the hair follicles were synchronous, the hair would all grow at the same time.  This would mean that there would be periods during which we would all be bald and other moments when we would have a full head of hair!    The period during which our hair actively grows is called the anagen phase. It lasts from 1 to 3 or 4 years. During this phase, the hair bulb, which is located at the bottom of the follicle, is regenerated and then produces a hair fibre. Our hair grows approximately 1cm per month.   The second phase is called the catagen phase or transitional phase, which lasts 2 to 3 weeks. This is the end of the hair fibre production phase, when the follicle retracts from the surface of the scalp. The hair stops growing, and remains in this phase for a few weeks before moving into the resting phase.

The third and final phase in our hair’s life cycle: the telogen phase, which corresponds to the resting period. The hair is no longer growing, but remains attached to its follicle for approximately 3 months. After this 3 month period, the hair starts to fall out when we wash or brush it.  A new anagen phase can now begin. Thus, our hair does not grow in a continuous manner, but in successive cycles. 90% of our hair is in a permanent growth phase, whereas 10 % is in an expelling phase. Each day, we naturally lose between 50 and 80 strands of hair, after a 2 to 7 year life cycle.  These strands of hair are then replaced by new hair.  Each hair follicle produces a new strand of hair in its growth phase, with a total of 25 to 30 cycles during our lifetime. However, sometimes our hair growth cycles may become interrupted, due to the influence of male hormones.

 

4.2-The hair’s life cycle in the light of science_illu-2