The fastest growing tissue of the body is hair. Hairs grow from roots which rest in hair follicles located in the dermis of the skin. The visible portion of the hair is called the shaft and is not alive like the root of the hair. The lair of skin surrounding the root of the hairs is called the dermal papilla and is fed with nutrients from the blood stream. New tissue, primarily composed of the protein keratin is added to the shaft which influences hair growth. The hair grow in three stages which can be called the phases or stages of hair growth. These are called:
These three stages act successively and have a set time period in a person with normal hair. The anagen phase (meaning to grow again) represents the phase of hair growth. During this phase the shaft of a strand of hair grows actively and the hairs get long before the onset of the next phase when the hairs fall out. This means that the length of the anagen phase determines that how long the hair will eventually become. The anagen phase is longer in women than men and is also longer for the hair of the scalp than the hair anywhere else on the body. It usually lasts about five years for normal hairs. The next phase is the phase called catagen (meaning to break the growth) in which the hair atrophy and fall out. It is a normal phase and it lasts for about three weeks. It is well known fact now that it is normal to lose hundred hairs per day. This is due to this catagen phase which serves to renew the hair and together with the anagen phase constitutes the ‘molting cycle’. All the hairs do not enter the catagen phase together so the hair loss is not noticeable until it becomes serious in some abnormality.
The last phase is the Telogen which represents a resting phase of the hair follicles when they are not growing. In case of normal healthy hairs, about ten percent of the hairs of the scalp are in the Telogen phase and the rest are in the other phases. The Telogen phase lasts about 12 weeks; after which the anagen phase ensues.
This was a brief introduction of the stages of hair growth. Understanding the intricacies of hair growth can be helpful in treating abnormal hair growth conditions.
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