The Phases of Hair Growth

Hair on our scalps grows about.3-.4 mm/day or about 6 inches per year. This hair growth and loss is completely random – and is not seasonal or cyclic. At any given time, a random number of hairs will be in various stages of growth and shedding.




There are three stages of hair growth which is important to know about. These are called: anagen (growth phase), catagen (transtional phase), telogen (resting phase).



Anagen – Anagen is the active phase of the hair (hair which is living and growing). The cells in the root of the hair are dividing rapidly. A new hair is formed and pushes the club hair up the follicle and eventually out. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2-6 years. Some people have difficulty growing their hair beyond a certain length because they have a short active phase of growth. On the other hand, people with very long hair have a long active phase of growth. The hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30-45 days explaining why they are so much shorter than scalp hair. Hair loss occurs when anagen is interrupted by certain medications (e.g. anti-cancer drugs), or by the ‘autoimmune’ disease, alopecia areata. Anagen hair is tapered or broken-off.



Catagen – The catagen phase is a transitional stage and 3% of all hairs are in this phase at any time. This phase lasts for about 2-3 weeks. During this time growth stops and the outer root sheath shrinks and attaches to the root of the hair. This is the formation of what is known as a club hair.



Telogen – Telogen is the resting phase and accounts for 10-15% of all hairs. This phase lasts for about 100 days for hairs on the scalp and much longer for hairs on the eyebrow, eyelash, arm and leg. During this phase the hair follicle is completely at rest and the club hair is completely formed. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. About 25-100 telogen hairs are shed normally each day, generally more in autumn or winter. Excessive shedding results in telogen effluvium, often a couple of months after an event such as child-bearing, fever, an operation, weight loss or certain medications. Sometimes there appears to be no recognisable cause, and the shortened hair cycle can continue for years (chronic telogen effluvium).



After the Telogen phase the cycle is complete and the hair goes back into the Anagen phase. New hair shafts form and older hair is pushed out and lost. The hair growth cycle then repeats.



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