What Causes Hair To Grow?
Hair growth results from cell division. To generate new hair living follicles, undergo three stages of growth: anagen, catagen, and telogen. When in the anagen stage, the follicles produce a whole hair shaft from top to base. The catagen and telogen phase is where the follicles reorganize and prepare the stem cells to obtain signals for a new growth cycle.
The hair growth cycle has an exceptional process of dormancy and activation, transitional periods of increased cell division, cell-fate decisions, differentiation, and apoptosis (natural death of cells) in the epithelial layer.
All this can be summed up in the three phases of hair growth.
Anagen is the phase where there is a rapid division in the cells at the base of the hair. A new hair emerges. It then pushes the older hair up and, in the long run, out of the follicle. In this active phase, there is an increase of about 2 cm every four weeks.
Hair growth in the anagen phase is different in different people. Some have a longer active period than others.
- Catagen
Catagen is a period of transition. At any moment, 3% of your hair is in the catagen stage. The stage lasts between 14 to 21 days. There is no more growth, and the outer root sheath contracts attaching itself to the root. And this is how club hair (non-growing hair) forms.
- Telogen
6-8% of hair is in the telogen phase at any time. It is the resting stage for the hair follicle. Eyebrows, eyelashes, and other body hair stay in this stage longer than scalp hair (about 100 days). The hair does not grow anymore, and in this stage, we shed about 25-100 hair every day.
In conclusion, hair growth is a complex process that takes time from the fetal stage. It is still difficult to establish why some people have longer phases than others, but more research is being done on hair growth, maintenance, and regeneration.