Laser hair removal can be divided into 3 categories:
1. Laser hair removal without selective damage, such as CO2 laser hair removal, which is time-consuming and easy to form scars;
2. Photodynamic therapy, such as oral or topical alpha-aminoacylpropionic acid followed by laser irradiation, seems feasible in theory, but has few clinical applications;
3. Selective photothermal hair removal, namely laser and intense pulse light hair removal.
The principle of modern laser hair removal machine is based on the principle of "selective photopyrolysis" proposed by American doctors Aderson and Parrish in 1983: A certain wavelength of laser passes through the epidermis and enters the dermis, selectively absorbed by the melanin particles in the hair and hair follicles, producing a photothermal effect, the heat energy in the hair is transmitted around, and the hair follicles and stem cells and other "hair roots" are completely destroyed, resulting in permanent hair removal. The normal tissue around the hair follicle does not contain melanin particles, so it does not absorb this laser, so it is very little affected, and generally does not cause paralysis marks.