Understanding The Hair Growth Cycle

In order to understand the causes of hair loss we need to explore the hair growth cycle.

There are three main stages to the hair growth cycle:

ANAGEN PHASE
The first phase is the growing stage. Hair grows at about 1.25 cm each month, and this phase can last between 2 and 7 years. Hair growth is very active during this period and division of the cells is rapid. Eighty-five percent of the hair on one’s head is in this state at any one time. Stress, disease and poor nutrition can potentially affect hair during this period and disrupt the growth cycle.

CATAGEN PHASE
Also known as the transition phase. As this phase begins the hair bulb detaches from the dermal papilla. the follicle shrinks and the hair shaft is pushed up. This period lasts for about two to three weeks.

This is the resting stage, during which there is no hair growth. This phase lasts about 3 months. At the end of the resting phase, the hair is shed (exogen), and the follicle starts to grow a new one. At any one time, only about 10% -15% of hairs are in the resting phase. It is normal to shed 50 - 100 telogen hairs on a daily basis.

Any disruption of of the hair growth cycle can result in hair loss. If there is an imbalance between the anagen and telogen stages, when more hairs enter the telogen phase prematurely, there results diffuse hair loss (telogen effluvium).

Follicles may temporarily fail to enter anagen after the telogen phase, which causes hair thinning. Hair thinning may therefore not necessarily be due to an increase in hair shedding, as can occur in the context of iron deficiency anaemia.

The development of androgenetic hair loss is seen with shortening of the anagen phase of the hair cycle with an increase in the proportion of telogen hairs.