Laser hair removal is based on the theory of selective photothermal action. In addition, the hair follicles and hair shafts are rich in melanin, and the laser can precisely and selectively depilate the hair with melanin as the target. After the melanin absorbs the laser energy, the temperature rises sharply, leading to the destruction of the surrounding hair follicle tissue and the hair removal.
In short, there is melanin in the hair follicles. After the melanin is absorbed, the hair will atrophy and fall off naturally.
When the hair follicle is destroyed, natural hair will not grow.
But the problem comes again. Why does laser hair removal take so many times?
Hair growth can be divided into four stages: growth phase, decomposition phase and resting phase. The hair mother cell divides rapidly during the growth period, during which melanin is the most, so it is extremely sensitive to laser light. In the anagen phase, the hair matrix degenerates, and the dermal papilla is atrophy; at rest, the hair follicle separates from the nipple, and the hair falls off. The rest time varies from part to part.
The relationship between hair growth cycle and hair removal treatment: Since laser has no obvious effect on hair in the anagen and telogen phase, laser can only work when these hairs enter the growth phase. Therefore, laser hair removal requires multiple treatments to make the effect obvious. If the proportion of hair in a certain part of the growth period is small, the number of treatments should be increased. Otherwise, the number of treatments can be reduced. Different parts of the hair have different growth cycles and different treatment intervals. If the hair rest period is relatively short, the interval can be as short as one month; and the rest period of the trunk and limbs hair is relatively long, so the treatment interval should be about 1 to 2 months.