Hair Growth Cycle
And The Factors
That Affect It...

• Anagen is the period of hair growth. Hair growth originates from the germinal matrix that surrounds the dermal papilla at the base of a hair follicle. Continuous cell division pushes older cells upwards and forms the hair shaft. As these hair cells reach a third of the way up a follicle, they start to die and harden.


• Anagen usually lasts between 3 and 5 years (but can vary as much as 1 to 7 years). The duration of anagen will determine the length to which hair can grow.


• The hair growth rate during anagen is usually about 3 mm per week.


• On average, 90% of follicles are in anagen at any one time.

• Catagen is the period of hair breakdown. Hair growth stops and the hair shaft detaches from the base of the follicle. This forms a club hair.


• Club hairs - When a hair follicle enters catagen, there is a surplus of hair cells in the hair root which needs to be removed. These remaining cells get attached to the end of the hair as a small lump of keratin. A club hair will often wedge into the follicle until it gets brushed or washed out. Instead, the club hair might stay in place until the follicle restarts the hair growth cycle and a new hair shaft pushes it out.


• As the base of the hair follicle breaks down, the follicle starts to shrink. However, as the follicle gets shorter, part of the outer root sheath (ORS) stays attached to the papilla cells ready for the next hair growth cycle to begin.


• Catagen lasts just 2 to 3 weeks.


• On average, 1% of follicles are in catagen at any one time.

• Telogen is the period of rest. During this time, the follicle stays shortened, and the ORS remains attached to the papilla forming the root germ. As telogen ends, the root germ starts growing downwards to form a new hair bulb around the dermal papilla and allows the next hair growth cycle to begin.


• Telogen lasts 3 to 4 months. When telogen ends, anagen restarts.


• On average, 10% of follicles are in telogen at any one time.

• The period of growth (anagen) and rest (telogen) varies from person to person, and can be affected by diet, health and age.


• The hair growth cycle is independent for each hair - whilst many other animals have hair growth cycle synchronisation to some extent, we do not. Cats, for example, moult heavily each spring, but we constantly lose between 100 and 150 hairs each day instead.


• The hair growth cycle applies to all hair types. However, hair growth rates and the duration of the cycle can vary in different parts of the body.
  
  For example, eyebrows will grow at a much slower rate than scalp hair, and their growth cycle is shorter too. This explains why eyebrows don't grow as long as do the hairs of the scalp. Body hair also grows slower than scalp hair.


• The growth cycle of hair is governed by chemical signals.