Hair Growth Cycle
Hair follicles normally exist in three phases of growth:
- A growth period called the Anagen phase, typically lasting three or four years, followed by
- A brief shriveling up period called the Catagen phase, followed by
- A dormant or resting period called the Telogen phase, usually lasting three or four months.
So, a normal hair follicle will typically grow for about three years and then rest for about three months, before regrowing a brand new hair strand. As the new hair grows and lengthens, it ejects the old hair strand resulting in the normal shedding of hair that we experience every day (we normally shed up to 50 or more hairs per day). This cycling will typically allow the hair shaft to grow about 18 to 24 inches (e.g. shoulder length hair) before it sheds. Some exceptional individuals have a naturally longer growth cycle and can, therefore, achieve much greater hair length (e.g. waist length hair).
Most of your follicles, approximately 90% to 95% (most people start out with about 100,000 hair follicles), are in the growth phase, growing approximately one half inch per month.
If your growth cycle is unusually short, the hair shaft won’t achieve much length. As mentioned, that’s one of the things that happens when the “Androgen sensitive” follicles within the pattern are continually exposed to normally present DHT.
Let’s recap and put it all together. Every hair follicle has a genetic code determined at conception. This genetic code controls “if” and “when” each follicle will become vulnerable to the hair killing effects of a normally present male hormone called dihydrotestosterone or DHT. When this happens, DHT begins to slowly diminish the now vulnerable follicles by:
- Causing Miniaturization, and
- Shortening the Anagen Phase
As a result, hair within the thinning or balding pattern becomes progressively finer, shorter, loses pigment, and sheds/cycles more frequently.
Telogen Effluvium occurs when large numbers of hair follicles prematurely cycle, entering the Telogen phase; this usually occurs in response to some physiologic change (e.g. medication change, fad diets, severe weight loss, after childbirth, etc.). This hair growth cycling abnormality frequently causes dramatic shedding when the dormant Telogen hairs begin to grow again, usually three months following the physiologic trigger. In some women, their follicles are hypersensitive to numerous triggers, causing constant Telogen Effluvium episodes. This condition is referred to as Chronic Telogen Effluvium and may be improved with lifestyle change and medication.