What is the hair growth cycle?

General Hair Loss

Knowing the different types of baldness is important in order to know how to treat it. Key to this is understanding the hair growth cycle and how it works

There is the very common androgenic alopecia that a majority of men experience in their early thirties. The autoimmune variation of alopecia such as alopecia areata, alopecia totalis and alopecia universalis also occurs to a certain degree though is less common.

These three forms mistake the hair follicles as foreign objects in the body and are attacked by the white blood cells causing hair loss. Fortunately, the stem cells that could help generate new hair are not attacked so it still has a possibility of growing back. Another form of alopecia is traction alopecia. This is neither genetic or is caused by an autoimmune reaction. It is simply the abnormal pulling of hair that makes it tightly wound causing gradual hair loss at the place of injury. Examples of these hairstyles are ponytails and cornrows.

hair growth cycle

Knowing what causes hair loss is only part of the story. It would also be helpful to find out what causes it to grow and a discussion of the hair growth cycle will shed more light on the topic.

There are three stages to the hair growth cycle and are known as the following: anagen, catagen and telogen.

The anagen stage is also known as the growth phase. Hair is very active during this phase and division among cells is very rapid. New hair is formed at this time and lasts for a period of two to seven years. The anagen stage is the one responsible for hair length. Eighty-five percent of hair on one’s head is in this state at any one time. Stress, disease and poor nutrition can materially affect hairs during this period and disrupt the growth cycle.

Next is the catagen stage also known as the transition phase. This period lasts for about two to three weeks. It is where the hair strand detaches from the dermal papilla and the hair follicle shrinks. That detachment from the dermal papilla is the time when club hair is starts to form.

The telogen stage is also known as the resting phase. This is the period where there is no hair growth for about three months. Ten to fifteen percent of the total hair on one’s head is in this phase at any particular time. It is also at this stage where club hair formation is complete. When hair is pulled out during this phase, one would notice a hard, dry and whitish material at its root. New hair starts to grow at this stage despite the old hair still resting.

The last stage is the exogen stage or the new hair phase. Not much is usually discussed about this as only the first three stages are often mentioned. What happens here however is that about fifty to one hundred telogen hairs shed everyday. This is a normal occurrence as the old hair from the telogen stage is replaced by the new.

Going back to hair loss, it occurs when there is an imbalance between the anagen and telogen stages. That is, where the eighty-five percent to fifteen percent ratio is not met. The causes that lead to this hair loss are discussed above.

On a cellular stage however, hair loss occurs when the hormone testosterone binds with the enzyme 5-alpha reductase to create a more potent hormone called dihydrotestosterone (DHT). This hormone is responsible for the maintenance of the male reproductive system. It also causes the hair loss by attaching to the androgen receptors of the hair follicle. The DHT blocks the nutrients from getting to the hair follicle, causing it to shrink and resulting in the hair loss.


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