Qu'est-ce que l'épilation laser et comment ça marche?

Hair removal with the use of laser is based on selective photothermolysis.

The target tissue (that is the hair) absorbs light-energy of very specific wavelength resulting in the sudden rise of temperature with an ultimate goal its destruction but also of all the regenerative structures of the hair follicle (stem cells, bulb melanocytes, nipple and bulge point ).

The temperature the hair follicle develops is 70 centigrade. But which is the right radiation wavelength? Below  600nm the penetration depth of the radiation is always smaller than 1mm but also the more the wavelength increases, the more the penetration ability of the laser ray increases.  Hence the bigger the wavelength ,the more effective it is in the destruction of deeper hairs  (e.g. at the back ). The disadvantage though of a big wavelength  (e.g. 1100nm) is that it doesn’t catch well the small and superficial hairs and it hurts more because it goes to deeper structures of the skin. Melanine is effectively absorbed in the area of the electromagnetic spectrum between 600nm-1100nm. Below 600nm, they strongly absorb the blood vessel and bigger than 1100nm they are strongly absorbed by water.  Therefore, these wavelengths are forbidden and cannot be used for hair removal.

The wavelengths available for hair removal using laser, at the spectrum range between 600nm-1100nm are:

• 694nm (Ruby laser)
• 755 (Alexandrite laser)
• 800-810nm (Diode laser)
• 1064nm (Nd:YAGlaser)
• 600-1100nm (IPLs-wide spectrum pulse light sources ). 

In order for the hair removal with laser to be effective the following conditions must be fulfilled and taken into consideration: 

The three key points on the hair follicle that must be destroyed (all three of them) and include melanine are: the bulb, the nipple, and the bulge point.

Hair removal with laser must take place at the regenerative developing stage of the hair because then melanine is at higher concentration, the hair has a small size, it has more superficial place and it is more vulnerable to radiation than laser at this stage.

That is why sessions are arranged every 6 weeks to find them at his stage.

Thus, when the hair is destroyed at the regenerative stage, we need less laser sessions and the overall destruction duration of the hair lasts less time. The type of hair on which laser is applied must be the final hair , meaning the darker, harder and blacker the hairs are, the more intensely they absorb the laser radiation and the faster they are destroyed. The density and the depth of the hair depend on the part of the body it is. That is why the wavelength of the laser must be ideal to reach the right depth. Also, the duration of the developing stage of the hair depends on the body part.  The smaller the developing stage a hair has, the sooner the session must take place. This also explains why not all the hairs in different parts of the body aren’t destroyed at the same time.