The Wise Book of Whys by Daven Hiskey & Today I Found Out.com

Author:Daven Hiskey & Today I Found Out.com [Hiskey, Daven]
Language: eng
Format: epub
Publisher: Vacca Foeda Media
Published: 2013-12-08T11:00:00+00:00

Why Hair Only Grows to a Certain Length

Hair length is completely controlled by the length of the anagen phase of your hair follicle. How long this phase lasts is determined mostly by genetics, but it can also be affected by hormones and extreme stress. But in the end, there is a chemical signal that ultimately controls the exact growth cycle.

Following the anagen phase is the catagen phase. It isn’t yet known what triggers the catagen phase, but once it is triggered, the outer part of the root is cut off from its nutrient supply (blood), as well as the cells that produce new hair, thus your hair stops growing. This phase lasts about three weeks.

Next up comes the telogen phase where the follicle is in a resting state and your hair is now a “club hair,” completely dead down to the root. During this stage, these hairs are relatively easy to pull out (as can happen while brushing/combing/washing your hair), but if they manage to last long enough, they’ll eventually be pushed out by a new hair as the cycle begins again.

Obviously hairs on your arms or legs have a very different anagen period than hairs on your head, thus why your leg hair doesn’t grow two feet long without trimming. Further, different people, thanks mostly to their genetics, have differing lengths of the anagen period for a given body part compared to other people. For the hair on your head, the average length of the anagen phase is about 2-7 years. For your arms, legs, eyebrows, etc., this phase usually lasts just 30-45 days. However, in extreme cases which are quite rare, some people have anagen periods for their heads as short as most people’s anagen phases for their arms and legs. For these people, their hair never naturally grows more than a few inches long. The opposite is also true for people whose anagen phase can last decades for their scalp hair.

At any given time about 85 to 90 percent of your hair is in the anagen phase, 1 to 2 percent is in the catagen phase, and 10 to 14 percent is in the telogen phase. However, extreme stress can trigger the anagen phase to stop prematurely and hair can rapidly progress to the telogen phase, even as much as 70% of the hair on your body. When this happens, the majority of your hair that should still be growing can fall out all at once.

Under normal circumstances, though, you can get a rough estimate of how long your anagen phase is based on how long your hair grows naturally without cutting off a given area. First, assuming your hair isn’t already as long as it can get, measure your hair length, then exactly a month later measure it again and note the difference. Now you have your growth rate (usually about 1 centimeter every 28 days or 1 inch every 71 days). So if, without cutting, the hair on your head eventually grows 16 inches long max, then your anagen phase lasts: (inches*period per inch).

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