How Does Hair Grow?
A full, healthy head of hair consists of about 100,000 - 150,000 individual hairs, and only 90% of those hair follicles are usually in a stage of growth. The remaining is either resting or transitioning.
Hair growth is divided into three phases: anagen, catagen, and telogen.
- Growing (anagen)
Every hair on your head is constantly going through one of the three stages of the hair growth cycle. The first phase is a growth phase, called anagen, and it can last anywhere from 2 to 6 years. While in this phase, the group of cells at the base of the hair, called the dermal papilla, multiply rapidly. As new cells form, the old ones move upward creating the hair you see. The longer it lasts, the longer the hair grows. Normally, around 80 to 85 percent of the hairs on the head are in this phase.
- Transitioning (catagen)
The cells at the base of the hair stop multiplying, the hair stops growing, and it enters into catagen or the transition phase. This part of the hair growth cycle only lasts from 2 to 3 weeks. It allows the hair follicle to renew itself.
- Resting (telogen)
Finally, the hair enters a resting phase called telogen. The follicle lies dormant for 1 to 4 months. Normally between 12 and 20 percent of hairs are in this phase. Under times of tremendous stress, many follicles can be “shocked” into this phase simultaneously and then shed in a short period (telogen effluvium).
- Growing again (anagen)
After the hair has been shed, a new hair begins to grow, and the cycle repeats itself — through anagen, catagen, and telogen — for each hair follicle on your head for as long as it is active.