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Each hair shaft grows out of a hair follicle located in the epidermis, the outermost layer of
skin on the scalp. The scalp consists of a great number of individual hair follicles,
each working independently. Deep within the hair follicle two substances are generated: a
protein named
Keratin
of which the hair is formed, and a Pigment called
Melanin
which dictates the colour of the hair. The quality of the growing hair is dependent on
the amount of keratin generated within the hair follicle. A sufficient quantity will generate
thick, strong hair. Lack of keratin will result in weaker and thinner hair.
The growth cycle of the hair consists of 3 phases:
1. Anagen - The growth phase:
during this phase, keratin is generated at the base of
the hair follicle and forms the hair shaft. It lasts about 5 years, and 90% of all hair follicles
are in this phase at any given time. The exact length of this period varies from one
person to another depending on several factors such as age, race, health etc.
2. Catagen - The resting phase:
The hair shaft stops growing and its root shrinks. It
begins to slide out of the shrinking hair follicle, moving further away from the blood
vessels supplying it with the amino acids, vitamins and minerals needed for the
generation of the keratin and melanin. With time, the hair shaft will just fall out of the follicle.
This phase lasts for anywhere between a few days to two weeks. Only a few percents of
the follicles are in this phase at a time.
3. Telogen - The regrowth phase:
The hair follicle returns to its normal state and the
formation of a new hair shaft begins. If by this time the pervious hair shaft did not
slide out of the hair follicle, it will be gradually pushed out by the new growing hair shaft.
The duration of this period is a few months.
Losing fifty to a hundred hairs a day is considered normal.
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