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What is the hair cycle and what are its phases?

28 October 2021


How does the hair cycle work? | Clínica de Freitas

Human hair is in constant development and renewal, through a cycle that goes through different stages. In this article we will talk about the hair cycle and how it affects the birth, growth and loss of hair.

When caring for and treating your hair, you should know that it is normal to observe hair loss. Every day, every hair is in some phase of the hair cycle, which means that some hair will be growing, some will be at rest and some will fall out.

Each hair goes through its cycle independently of the others. Therefore, every day new hairs grow on the scalp, while others fall out and this hair cycle restarts continuously.

What is the hair cycle?

The hair cycle is the path and evolution that hair goes through from its birth to its fall. In each hair cycle, hair is born, grows, rests and finally falls out, being replaced by a new hair strand.

The hair cycle can last a variable length of time, depending on the age of the person, the part of the body where the hair grows and the type of hair or vellus hair in question. On the other hand, as mentioned above, the hair cycle in humans is not synchronized, so every day there will be hairs that are born and others that fall out.

Thus, each hair follicle goes through approximately 25 to 30 hair cycles in a lifetime. This should not alarm you, the number of hairs that are in the growth phase is always greater than the number of hairs that fall out. If the scalp is healthy, it has approximately 100,000 hairs, 86% of which are growing.  

Phases of the hair cycle

The hair cycle is divided into 3 distinct phases. In each of them, the hair will perform a different task and undergo specific changes.

The phases of the hair cycle are:

  •  Anagen phase: This is the first phase of the hair cycle and is the moment when hair is born and grows. As mentioned above, approximately 80% of the hair on the scalp is in this stage and grows about 1 centimeter per month.

During the anagen phase, the follicles are metabolically very active, which makes them considerably sensitive to nutritional or chemical changes that may affect them. 

This phase is the longest of the three phases and can last from 2 to 5 years in scalp hair.

  • Catagen phase: The catagen phase is the shortest stage of the hair cycle and lasts approximately two weeks. Consequently, the number of follicles that will be in this phase each day is very small.

During this stage, the hair bulb is separated from the bloodstream and no longer receives the nourishment it previously collected. Consequently, the hair stops being nourished and stops growing, entering a resting phase.

  • Telogen phase: The telogen phase is the hair loss stage par excellence. With this phase, the hair reaches the end of its cycle and is the moment when it falls out, being replaced by a new hair that will grow from the hair follicle that is still under the skin.

This stage marks the end of the hair cycle and lasts between 2 and 3 months. Once the hair falls out, the cycle begins again with the birth of a new hair.

Alterations of the capillary cycle

As we already know, the hair cycle is a continuous process that repeats itself over and over again, constantly renewing a person's hair. As each hair fulfills a cycle independent of the rest, every day we will have hairs in each of the stages mentioned.

Consequently, it is normal to observe a hair loss of approximately 50 to 100 hairs per day. This represents the hairs that enter the telogen phaseevery day and fall out.

However, there are some factors that can intervene and alter the normal hair cycle. When this happens, we can observe a higher level of hair loss, decrease in hair density, deterioration in hair quality or bald areas, among other symptoms.

Among the factors that can modify the hair cycle are hormones, which regulate different body processes and are capable of changing the development of the hair cycle.

Sex hormones, such as testosterone, actively intervene in the hair cycle. This is a hormone found in both men and women, and its derivatives (Dihydrotestosterone or DHT) have the ability to modify the hair cycle and prevent normal hair growth.

When this happens, the hair is depleted and gradually becomes thinner until it takes on the characteristics of body hair or stops growing altogether. This process is called miniaturization and the condition that causes it is known as androgenetic alopecia.

Androgenetic alopecia is a type of chronic hair loss that is difficult to reverse. This means that currently there is no definitive cure, but it is only possible to stop its progression through different hair treatments.

Androgenetic alopecia should not be confused with hair loss caused by temporary effluvium or seasonal hair loss, both phenomena caused by different causes.

Myths about hair growth

In addition to knowing the common hair cycle, some people assume that the lunar calendar can act and modify normal hair growth. This would imply that the position of the moon may exert some influence and may or may not favor the development of follicles.

The effects of the moon on the hair cycle have not been scientifically proven. However, specialists are actively studying this possibility. 

On the other hand, many men and women avoid wearing caps or hats, motivated by the belief that these accessories prevent proper oxygenation of the hair. This assumption is not true either, as the follicles obtain the necessary oxygen and nutrients from the bloodstream. 

What to do when the hair cycle changes?

Any change in the hair growth cycle is observable through the appearance of the hair. The hair may look thinner, weaker, notice a greater amount of hair loss or see that the overall density of the hair has decreased.

As we have mentioned in this article, these alterations in the hair cycle can be due to different causes. Therefore, before starting a hair recovery treatment, it is necessary to perform a personalized hair analysis and diagnosis.

Only by knowing the causes of the present hair problem, it will be possible to treat it effectively and stop hair loss.

At Clínica de Freitas, a center specialized in hair health founded by Dr. Rafael de Freitas, you can request a first consultation free of charge. In this instance you will know not only your hair diagnosis but also the solutions for your hair loss and your suitability for a hair transplant if necessary.

Do not resign yourself to losing your hair. At Clínica de Freitas it is possible to recover your hair and get back the look you have always had.