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Hair and its life cycle

Whether we are a man, woman, young or old, we are all more or less covered in hair from our head to our toes. Underarms, scalp, legs, back, face, pubis and even our arms, no area of our body is hair free. Hair is one thing we all have in common, but its life cycle varies depending on several factors.

First of all, what is a hair? (see diagram)

In this bubble the bulb, the base and only living part of the hair, is formed. When it grows, the hair shaft grows out of the skin, and this is the only visible part of the “keratinized” hair. A hair is a kind of shaft, with varying lengths, and it is hard and thick, depending on the area of the body and the person; it is formed in a small bubble under the skin, which is called the “hair follicle”.

What is its life cycle?

The sebaceous gland determines the length and life cycle of the hair and also protects it. Hormones are a decisive factor and they act on this gland and influence its sebum secretion level. As a result, the more sebum is secreted, the more the cycle speeds up, and the shorter the hair life cycle becomes.

The hair life cycle is affected by several criteria:

  • the area of the body
  • the type and nature of the hair
  • A person’s characteristics, such as their age, weight, sex, metabolism, origin, hormones, etc.

Certain external factors also influence its life cycle, including the food we eat, the drugs we take and the environment in which we live.

While the length of the hair life cycle is different in each person, its chronological system, which is divided into 3 phrases, is the same for everyone:

1. The anagen phase:

This is the final hair growth stage, during which its pigmentation is determined, and its melanin concentration is at its highest. This phase lasts several years, and up to 85% of our hair is in this phase at any one time.

The hair’s root lives in the bulb, an area located 1.5 mm under the skin, and will grow from it.

Before entering the catagen phase, the hair experiences some disruption, the papilla gradually changes and melanin production stops in the germinal areas.

2. The catagen phase:

This is a transitional period in the life of a hair and is also called the hair regression stage. It lasts around 2 weeks, and the hair stops growing. Around 3% to 4% of our hairs are in this phase at any one time.

3. The telogen phase:

This is the hair’s actual resting phase, called “cell rest”, and it lasts between 5 and 6 weeks, before the hair falls out. Around 13% of our hair is in this phase at any time during our life. The hair stops growing completely and falls out. Its life cycle ends to let a new hair grow in its place.

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