Sessions frequency: understanding the hair cycle

Every hair develops according to a cycle divided into three phases: the young and adult life (anagen phase), the oldness (catagen phase), and the death and fall (telogen phase).

We have seen that it is the accumulation of heat in the hair stem and bulb that induces hair destruction. In the anagen hair, the stem is attached to the bulb, which is full of melanin. Anagen hair are our real targets. Of course, it will be impossible to destroy all anagen hair at 100% in one session (it depends on the power of the shot, and on the hair’s intrinsic repair capacity).

Hair physiology

As all the hair in a same area are not in the anagen phase at the same time (only 20 to 60% of the hair depending on the areas), permanent hair removal of all the hair will only be possible after several sessions, once all the hair are caught in their anagen phase. According to areas, maintenance sessions might be necessary times to times.

Anagen hair are full of melanin in their base. During the laser shot, the melanin beam absorption (the pigment determining hair colour) will generate an intense heating (80°C approximately) of the bulbs. This heat will then spread throughout the bulb, and in the germinal cells notably, which will be damaged by such a significant and sudden elevation of the temperature. After several sessions, the injuries accumulated become irreversible, and a permanent hair removal of the area treated is obtained.

Catagen hair contain much less melanin. The heat delivered by the laser flash at the bulb level will not be important enough to damage significantly the germinal cells. The hair will fall after the session, but injuries on the reproductive system of the hair will not be severe enough to destroy it.

Telogen hair are already falling, and damaging the germinal cells of the bulb is hardly possible.

Deducing the treatment frequency

The physician's duty is to obtain the best results possible with as few sessions as possible. The regrowth will be weakened as soon as after the first session, but the battle is not yet won: hair do not give in so easily! The following sessions are meant to damage the repair mechanisms of the hair, until lesions become irreversible.

An average of four to five sessions suffice to obtain impressive results, but the utmost skill of the physician consists in determining a frequency of sessions as efficient as possible.

Frequency based on the understanding of the hair life cycle

It is only after years of experience that we managed – my team and myself – to find a treatment we were completely satisfied with. One of the keys was to understand that the duration of the hair cycles as they are defined in reference books are “theoretical” values and that they correspond to a hair “on rest”.

When the hair is attacked, like after a laser shot for example, it “drives crazy” and reproduces itself much faster.

This is why the first sessions are quite close in time, approximately two to three weeks between the two first sessions.  Then sessions become less frequent, and depend on a possible hair regrowth.

In men, the hormonal stimulation, as well as a deeper root, can make it more difficult, so that the treatment can last 12 to 18 months approximately.