Understanding the 3 phases of hair growth

Jonathon Graff

Run a comb through your hair and you might find a few hairs left behind in the teeth. If you see this happen every day, you might start to wonder if it’s normal that your hair is constantly falling out.

Shedding hair is absolutely normal, and just part of a hair’s normal growth cycle. Hair grows in stages, with a long stretch of active growth followed by a period of shedding and then a period of dormancy. This repeats throughout a hair follicle’s life, with each one independently growing at different stages.

To better understand how your hair grows – and what causes it to fall out – let’s examine what happens during each of the three phases.

1) The anagen phase: The longest phase of the growth process is called the anagen phase, or the active growth cycle. This stage typically lasts between two to six years, when the follicle is active and producing new cells resulting in hair growth at a rate of approximately one-half inch per month.

Each follicle’s anagen phase is on its own clock. Since the period of active growth varies from person to person, individuals with a long anagen phase can grow their hair much longer than those with shorter anagen cycles.

2) The catagen phase: This transition cycle marks the end of active growth, preparing the follicle to shed the hair that has grown during anagen. The hair detaches slowly from the bulb, the hair shaft falls, and the follicle enters a dormant period. Catagen is the shortest phase of the growth cycle, lasting only about two to three weeks.

3) The telogen phase: After shedding the hair shaft, the follicle rests and prepares for another round of the anagen period. This dormant phase lasts between two to three months before the cycle begins again with the active growth, anagen phase.

Why hair loss occurs
Hair growth is a chemical process governed by hormones and the rate of cell division. People with a genetic predisposition for hair loss simply experience hormonal changes that trigger a shorter anagen phase resulting in shorter, thinner hair.

If a person’s hair follicles are genetically susceptible, these hormones can increasingly constrict the period of new growth and the anagen cycle continues to shorten over time. This is why men and women lose their hair gradually, often over many years.

Fortunately, people don’t shed all of their hair at once, go through a few months of baldness and then grow it all back. Instead, like trees which don’t drop all their leaves in one season, men and women experience constant growth and shedding throughout the lifespan of the hair follicles they have. For this reason, hair restoration treatments are most effective when the follicles may have been damaged or rendered less effective but are still alive. Low-level light therapy (LLLT), for example, helps repair damaged follicles by exciting the cells, allowing them to divide more effectively and leading to better overall hair growth.

Unfortunately, no known hair loss regimen will bring a dead follicle back to life so any area that’s “shiny bare” won’t see much result regardless of treatment. Since the only option for completely replacing a dead hair follicle is surgical hair transplantation, it’s a good idea for anyone noticing thinning hair to look into treatments early rather than waiting until their follicles are beyond help.


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