Understanding Hair Growth

Hair growth occurs continuously as new hairs are formed at the base of the follicle and molded by a structure, known the inner root sheath, that surrounds the growing hair shaft. Androgens, the male sex hormone (actually present in both men and women) activates specific targeted areas of the body to produce hair.

Hair growth varies greatly between different people and the specific part of the body. Scalp hair, as an example, grows an average of one-tenth of an inch every week. Leg hair, by contrast, only grows at about half that rate.

The life cycle of hair follicles, the repeating cycle of growth and rest stages, affects hair production. No new hair follicles are produced after your birth – the appearance (and loss) of hair is the result of changing ratios in the growth and rest phases. This life cycle is distinguished as three separate stages: anagen, catagen and telogen.


The cycle of life for each hair follicle begins with the anagen phase — the re-starting of the follicle’s active stage where a newly formed hair begins to grow. This duration of this growth phase can be as short as several weeks (like the moustache) or as long as several years (as in the scalp area). So depending on the part of the body, hormones, and gender amongst other factors, duration of growth will vary.

But finally the level of growth begins to slow down. This second stage of slowing (and later arrested) growth is known as the catagen phase. This slowing will continue into the third, final phase — a period of inactivity where the follicle is in rest.

During this third stage, the hair will separate from papilla and is no longer able to be nourished. At this point, no more new hair cells are formed and the inactive hair remains held in place only by a thin strand of epidermal cells and can be shed by brushing, combing or other tension placed upon it.

The hair shaft remaining in place at the end of its growth cycle is called a club hair. It is not uncommon for a club hair to remain in place while a newly formed anagen hair is beginning to emerge, forcing the club hair to be shed.

Whether the club hair is shed or not, the hair follicle will once again become active and begin to grow a new anagen hair. This process of growth and rest continues throughout our lifetime. In humans, follicle activity is generally spread between all phases of the life cycle. Other mammals have a more orderly growth pattern, which shows as noticeable periods of hair growth and shedding.