The hair life cycle: understanding the anagen, catagen and telogen phases

The phases of the hair cycle

Our hair is constantly renewing itself and follows a precise cycle.

A hair appears, grows, and falls out, according to a hair cycle that repeats itself approximately 25 times during a lifetime.

This cycle is divided into three successive stages.

The hair grows: the anagen phase

The hair growth phase is called the anagen phase. It lasts approximately three years in men and five years in women.

It is characterized by intense metabolic activity in the hair bulb, leading to the formation of keratin, an essential protein that makes up the hair.

The matrix cells within the hair bulb multiply rapidly to form the hair fiber and its protective sheaths.

Under normal conditions, approximately 85% of the hair is in the anagen phase.

The vascular network in the scalp that nourishes the hair root is particularly well-developed around the follicle during this stage.

The bulb is large, dark, and surrounded by translucent epithelial sheaths.

This phase is regulated by hair follicle growth factors, which are necessary for healthy and strong hair growth.

The hair stops growing and dies: the catagen phase

Next comes the catagen phase, also known as the regression phase. It is fairly short, lasting only 2 to 3 weeks, and affects about 1% of the hair.

This is the transition phase between the growth phase and the resting phase.

Through a process of programmed death, the hair follicle regresses, shrinks, and becomes inactive. The physical link between the follicular papilla and the bulb is broken. The matrix dies, and although the hair no longer grows, it remains rooted in the follicle for a little while longer.

The hair falls out: the telogen phase

Before falling out, the hair is in a resting phase known as the telogen phase.

This phase lasts 2 to 3 months.

The dead hair remains anchored in the follicle for about 3 months. It has detached from the follicular papilla and slowly moves towards the surface of the scalp until it falls out.

It falls out when it is pushed out by a new, young hair, for which a new anagen phase begins.

This renewal period affects 14% of the hair.
 

What happens during reactive hair loss?

In case of reactive hair loss, there is a sudden and rapid transition from the anagen phase to the catagen phase, followed by the telogen phase. As a result, the hair suddenly enters the shedding phase.

Approximately 3 months after the imbalance or traumatic event that causes this premature transition to the telogen phase, hair sheds in noticeably greater amounts. This three-month period corresponds to the duration of the telogen phase itself: the time it takes for the hair to move from the moment it detaches from the follicular papilla to its expulsion from the scalp.

This type of hair loss is temporary and does not lead to baldness. By quickly reactivating a new hair cycle, it is possible to effectively slow down the loss and stimulate new hair growth.
 

What happens during progressive hair loss?

In the case of progressive hair loss, or androgenetic alopecia, it is a hormonal imbalance, specifically involving male hormones, that triggers an acceleration of the cycles.

This imbalance causes a disruption in the hair cycle and significantly shortens the anagen phase in both men and women.

As the growth phase is shorter, the hair enters the catagen phase and then the telogen phase too quickly. This is why we talk about the cycle becoming accelerated. The hair life cycles follow one another at a rapid pace.

The natural hair reserve, normally designed to last a lifetime. If this accelerated process is not slowed down, it leads to irreversible baldness.