The average adult head has about 100,000 to 150,000 hairs.
Normally the adult loses up to 100 of them a day.
At any one time, about 90% of the hair on a person's scalp is growing.
Each follicle has its own life cycle that can be influenced by age, disease, and a wide variety of other factors.
This life cycle is divided into three phases:
Anagen -- active hair growth that lasts between two to six years
Catagen -- transitional hair growth that lasts two to three weeks
Telogen -- resting phase that lasts about two to three months; at the end of the resting phase the hair is shed and a new hair replaces it and the growing cycle starts again.
Check the video below illustrating the life cycle
As people age, their rate of hair growth slows.
There are many types of hair loss, also called alopecia:
- Pattern hair loss, is known as male-pattern hair loss (MPHL) when it affects males and female-pattern hair loss (FPHL) when it affects females.
In males the hair loss often presents as a receding hairline while in females it typically presents as a thinning of the hair
Classic male-pattern hair loss begins above the temples and vertex, or calvaria, of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a 'Hippocratic wreath', and rarely progresses to complete baldness
Female-pattern hair loss more often causes diffuse thinning without hairline recession; similar to its male counterpart, female androgenic alopecia rarely leads to total hair loss.
- Telogen effluvium is temporary hair thinning over the scalp that occurs because of changes in the growth cycle of hair. A large number of hairs enter the resting phase at the same time, causing hair shedding and subsequent thinning.
- Scarring alopecia result in permanent loss of hair. Inflammatory skin conditions (cellulitis, folliculitis, acne), and other skin disorders (such as some forms of lupus and lichen planus) often result in scars that destroy the ability of the hair to regenerate. Hot combs and hair too tightly woven and pulled can also result in permanent hair loss.
- Alopecia areata is a chronic inflammatory disease which affects the hair follicles and sometimes the nails. Alopecia areata usually presents as patches of hair loss on the scalp but any hair-bearing skin can be involved. The nails are involved in about 10% of patients referred for specialist advice.
- Alopecia totalis, AT loss of hair from all the entire scalp
- Alopecia universalis hair fall out, including the eyebrows, eyelashes, and pubic hair
- Trichotillomania, the most frequently in children, it is a psychological disorder in which a person pulls out one's own hair.