hair lifecycle

Hair lifecycles

To understand alopecia, it’s necessary to understand the hair’s cycles thoroughly, which are divided into three phases:

  1.  Anagen phase. This is the first and longest of the three phases. In this period of growth, the hair fibre develops from the root of the hair.
  2. Catagen phase. This is the second phase, lasting about 4 weeks,  where hair growth slows down.
  3. Telogen phase. This is the final phase of the hair life cycle.
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This natural process is known as the “hair cycle.” To better understand, it is essential to know what hair consists of:

The outer layer of the skin through which the hair grows once it reaches a certain length is called the epidermis. It is the most widely known concept, along with the follicle, which is the part of the skin where hair growth occurs. There’s also the sebaceous gland, which are basically secretory organs that produce a fatty substance called sebum, found inside each follicle. Inside the follicle, there is also the root of the hair, which, along with the stem, is responsible for hair growth. All these components of the hair cycle are sustained by the blood vessels found in the tissue, which provide “food” to generate and produce the hair.

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Phases of hair growth: anagen, catagen, and telogen

Once basic hair terms are clear, it is necessary to clarify that the average life of a hair is between 2 and 7 years, and each hair follicle produces a new hair that grows in cycles until it falls out, each with its own life cycle.

This means that every hair grows completely independently of the others, which prevents times of total baldness or complete growth. This period of hair growth is called the anagen phase, and it can last up to 4 years. Inside the hair follicle is the hair bulb where the new hair is generated, growing approximately 1 centimetre per month. After this phase is a transition phase called the catagen phase, lasting no longer than 4 weeks and when the hair finally stops growing. During those weeks, the hair remains unchanged.The telogen phase is the last phase of a hair’s life, when the hair falls out. The follicle begins its rest by ceasing to function entirely. Hair no longer grows and stays attached to the scalp for at least 3 months. After that period is when it falls out. Every day, we naturally lose between 50 and 90 hairs. That is only 10% of all the hair we have, so most of them are in the anagen phase (the main phase). Throughout our lives, hair follicles can complete up to 30 complete cycles. When hair falls behind these growth statistics for different reasons, as explained in previous posts, is when baldness occurs.