How laser hair removal machines work

Laser hair removal methods can be divided into 3 categories:
1. Laser hair removal without selective damage, such as CO2 laser hair removal, is time-consuming and prone to scarring;
2. Photodynamic therapy, such as oral or topical α-aminocaproylpropionic acid followed by laser irradiation, this method seems feasible in theory, but has little clinical application;
3. Selective photothermal hair removal, namely laser and intense pulsed light hair removal.

The principle of modern laser hair removal machines is based on the principle of "selective photothermolysis" proposed by American doctors Aderson and Parrish in 1983: a certain wavelength of laser light passes through the epidermis, enters the dermis, and is selectively absorbed by the hair and hair follicles. The melanin granules of the hair are absorbed, resulting in a photothermal effect, and the heat energy in the hair is conducted to the surrounding, completely destroying the "hair roots" such as hair follicles and stem cells, resulting in permanent hair removal. The normal tissue around the hair follicle does not absorb the laser because it does not contain melanin particles, so the effect is very small and generally does not cause paralysis.