Why does hair stop growing after reaching certain length?

People around the world have different types of hairs, both in color and character. Some have curly hair while others have it straight. The color of the hair varies from black to red, mostly depending on the presence of a pigment named melanin. And, the length of the hair is a subject most of the people are found to be obsessed with. They compare the rate of growth of their hair with that of others and search for ways to increase it.
The rate of the hair growth is mostly determined by genetics and the lifestyle and the environment one is living in. The average growth rate is 6 inches per year. Stress and bad habits can affect the hair growth severely.
The hair follows a definite growth cycle consisting of three distinct phases namely anagen, catagen, and telogen. These phases occur concurrently and each of our hair strands is in one of these phases at a specific time. These phases are triggered by some unknown chemical signals.
Each of the hair grows from its own hair follicle, a skin organ that produces the hair. The length of the first phase of the growth cycle, anagen phase, is what determines the maximum length a hair strand can reach. How long this phase lasts is mostly is a genetic factor, but can also be influenced by hormones and health.
The anagen phase, also called growth phase, normally lasts between two and six years. During this period, the cells in follicle split to form new hairs and nourishment takes place. The longer the hair stays in this phase the longer it would grow.
The next is catagen phase, also called transitional phase. During this phase the follicle shrinks to one-sixth of its length, the hair is cut off from nourishment and the shaft is pushed upwards. Two weeks is the average length of the catagen phase.
During the next phase, telogen, the follicle remains inactive. This phase, also called resting phase, lasts about four months. The hair strands are dead in this period which can be shed with external force or with the emerging of new hair strands. Once the telogen phase ends, the new growth cycle begins with the anagen phase.
At a specific time, about 85% hair on a person’s head is in anagen phase while 1% is in catagen phase. About 10- 15% of the hair is in telogen phase. The hairs on various parts of the body have different lengths of anagen phase. The body hair has very short length of the phase which is the reason for they are short.

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