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What is the Hair Growth Cycle?

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  • Written By: T. M. Robertson
  • Edited By: Daniel Lindley
  • Last Modified Date: 02 November 2016
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The term hair growth cycle is used to describe the natural pattern of growth and rest experienced with hair. Within the hair growth cycle are three different phases. Anagen, otherwise known as the growth phase, is when the hair is in a growing cycle. The next phase is called catagen; this is the degradation phase, when the hair follicle is degraded and nonproductive. Telogen is the third phase, during which the hair follicle rests and fails to grow or degrade. Over the course of a lifetime, this hair growth cycle will repeat itself many times.

During the anagen phase, the hair follicle produces hair by binding keratin proteins to make individual hairs. As the hair follicle continues to produce more hair, the hair consistently gets pushed out away from the follicle, making the hair longer. This growth phase of a hair follicle typically lasts anywhere from two to eight years. Immediately following the growth phase is the catagen phase.

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When the hair follicle is in the catagen phase, it begins to degrade. This phase also serves as a transition period, when the hair follicle prepares itself for the telogen phase. The degradation phase is the shortest of all three phases and typically lasts between two to four weeks. During this stage, the growth cycle completely stops, and a type of hair called club hair is formed. It's only when the club hair is completely formed and detached from the follicle that the third phase, known as the telogen phase, will start.

The telogen phase is the part of the cycle when the hair follicle rests. The hairs in this phase are detached completely from the hair follicle. Normally, these are the hairs that people lose on a day to day basis when showering or combing their hair. On average, a person loses approximately 50 to 100 of these hairs every day. This phase typically lasts two to four months. Toward the end of this resting phase, the hair follicle forms a new hair and begins the anagen phase of the hair growth cycle all over again.

In an average adult, approximately 90 percent of hairs are in the anagen phase, 1 to 2 percent are in the catagen phase, and 10 to 15 percent are in the telogen phase at any given time. When this cycle is interrupted, it can result in either temporary or permanent hair loss. Extreme hair loss can be caused by a number of different things, such as chemical exposures, skin diseases, and genetic predisposition to baldness. When the hair growth cycle is interrupted by a temporary treatment such as chemotherapy, the hair will usually grow back and eventually go back to a normal hair growth cycle. If the cycle is affected by a more permanent condition, like skin disease, hair loss may be permanent.

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pastanaga
Post 3

@browncoat - The problem is that even if the hair growth cycle is shorter for some hairs than for others, it's still continual and I'm not sure there would be a way to discriminate between longer and shorter cycles.

I think the better solution would be for people to stop worrying so much about their hair in general. Body hair doesn't have to be that big of a deal if someone doesn't like having to remove it with conventional means.

browncoat
Post 2

@Fa5t3r - I've actually always thought this hair growth cycle is how scientists will eventually figure out how to prevent hair growth in places people don't want it. Generally the hair on your head grows the longest because it has the longest cycle, not because it grows any faster than the hair in other places. So if you can come up with a chemical that would only attack hair cells with a short growth cycle, you could remove body hair without harming the hair on a person's head. And since chemotherapy chemicals seem to be temporary in terms of hair removal, you wouldn't even have to commit to permanent hair loss.

I know chemotherapy drugs have a lot of other side effects, but if those could be mitigated, it would save a lot of time and money spent on hair removal.

Fa5t3r
Post 1

Apparently the reason that hair can be disrupted by chemotherapy is that the chemicals are designed to attack cells that are actively growing. One of the only ways to tell the difference between cancer cells and normal cells is that they grow continuously rather than growing and then dying off as they are supposed to. This is why they are dangerous and form tumors, because they just keep piling up in place.

Hair cells and stomach cells are two of the few types of cells that are always actively growing on the body, so they are attacked by the chemicals as well as the cancer cells.

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