1.The principle of laser hair removal

          The principle of laser hair removal is selective photopyrolysis, which uses light energy to selectively destroy hair follicles and make hair no longer grow. The hair follicle is rich in melanin. After the laser enters the skin, the melanin absorbs light energy and converts it into heat energy, which increases the temperature of the hair follicle until its structure is damaged, so that the hair follicle shrinks and no longer produces hair, achieving a permanent simultaneous surface depilation effect.

          2.Wavelength selection of hair removal laser

          According to Fitzpatrick skin classification, skin can be divided into six categories. Alexandrite 755nm is the gold standard for hair removal and is more suitable for Type 1-4 skin. Diode 808nm laser is suitable for Type 2-4 skin, and Nd:YAG 1064nm is more suitable for Type 5-6 skin.

          3.About the difference between 755nm and 808nm laser

          Alexandrite 755nm laser is the gold standard for hair removal. Compared with Diode 808nm semiconductor laser, it has a better hair removal effect on small hairs with light color (such as lip hair and hairline); the absorption rate of melanin at 755nm is higher than 808nm (as shown on the left). Figure), so the hair removal effect is better, and it is not easy to relapse after hair removal.

          4.Pulse width and laser energy density

          The thermal relaxation time of human epidermis is 3~10ms, and the thermal relaxation time of hair follicle is 40ms-100ms. In order to avoid damage to the epidermis and surrounding tissues, in principle, the pulse width should be between the two, namely 10~30ms. For hair follicles with large diameters For people with dark skin, the pulse width can be relaxed to longer.

          The choice of energy density is related to skin tone, hair color, and hair follicle size and depth. Experiments show that to completely destroy the hair follicles of the black hair shaft with a diameter of 50um and a depth of 3mm, a laser beam with a spot of 5mm and an energy density of 20J/cm2 is required. The principle of selection is: the lighter the hair color, the higher the energy density required; the greater the contrast between the skin color and the hair color, the higher the energy density, and the lower the energy density.

Further reading：808 diode laser hair removal advantages