Hair growth

gave the class on hair and how it grows in cycles? Well, your hair grows in 
cycles, some peoples cycles are longer than others and they shed faster and 
some are slower producing long hair. Between starting to grow and falling out 
years later, each hair passes through three distinct stages. These are so 
important that they have been given special names: anagen (the growing 
phase), catagen (the intermediate phase) and telogen (the shedding phase). 


Anagen (the growing phase) 
The anagen phase of a new hair starts at the moment it begins to grow. At 
that time there is very active growth in the hair bulb. This usually lasts 
for some years, generally between three and seven, without interruption. 
Human hairs grow at a rate of roughly 1/2 inch a month.
Hair may grow more quickly in winter than in summer. Hair growth varies 
with the season as a result of a change in the difference between hair 
follicles in the growing and shedding phases.
Pigment (melanin) is made in the hair bulb throughout this phase of the 
hair cycle. Less pigment is made in the hair of older people. This is why 
white hairs start to appear, even though the hair itself may still be growing 
strongly.
In some older people the hair cycle becomes shorter, the follicles 
gradually give up producing long, strong hair, and the hairs become thinner 
and shorter. The result may be a general thinning of the hair, or even a 
degree of baldness.
The anagen phase is followed by a short resting phase. 

Catagen (the intermediate phase) 
This catagen phase lasts for between two and four weeks in the human 
scalp. No pigment is made during that time, and the follicle stops producing 
hair. The base of the follicle moves upwards towards the surface of the skin.

Telogen (the shedding phase)
The telogen phase lasts for three or four months. This is the time at which a 
new hair begins to grow from the hair follicle. As it grows upwards the old 
hair will be shed naturally or may be pulled out, which happens easily and 
painlessly with telogen hairs. These are the hairs that come out when you 
shampoo or brush your hair.
Shedding is part of the normal process of the replacement of old hair with 
new. At any one time, around one in ten of the follicles on an individual's 
head are in the shedding phase.
The new hair emerges from the same opening at the surface of the skin as 
the old one, and the hair cycle begins again.
How long anagen lasts is determined genetically, and varies between the 
sexes and from one person to another. It is the length of this time that 
decides how long the hair will grow before it falls out. Anagen lasts between 
three and seven years in most people. 

The growing and shedding of hair as a whole seems to happen at random, but 
for each hair follicle the process is precisely controlled. No one knows for 
certain, however, exactly how the body controls these cycles. 
Plucking a hair from a follicle brings forward the next period of hair growth 
in that follicle.