Laser hair removal, once and for all

Laser hair removal plays a role in hair removal by destroying hair follicles. Melanin in hair follicles in the growth period is the most, and the light absorption from laser is the strongest. It is the best target of laser hair removal instrument. The more melanin, the more clear, the higher the hit rate, and the greater the damage to hair follicles.

Everyone yearns for a smooth skin, so there are many kinds of cosmetics and maintenance products, which are dizzying. However, there are many people trapped in the long hair of lips, hands and feet. In addition, in addition to axillary hair and pubic hair, in order to quickly and quickly remove these small hairs, the traditional depilation methods range from the simplest clip removal to shaving, cloth sticking, honey wax depilation Some people do not hesitate to try chemical depilation and electroacupuncture depilation. Their function is only temporary, and their common disadvantage is that hair regenerates quickly.

Although electrolysis and thermolysis can effectively destroy hair follicles, they are cumbersome and time-consuming, and have the disadvantages of low efficiency, low curative effect, obvious pain and possible scar. In order to effectively, conveniently and safely remove excess hair on the body surface, according to the principle of selective photothermal action, a variety of laser systems and strong pulse light source systems have been designed to significantly reduce discomfort when people receive large-area hair removal treatment, and minimize scar formation and other complications. Permanent hair loss can be achieved by using modern optical technology.

As early as the 1960s, Goldman first described the destructive effect of ruby laser on hair follicle melanin, but it was not used clinically. In the 1980s, ohshiro described hair loss after ruby laser treatment of pigmented nevus, but the epidermis was also seriously damaged. In 1993, Wilman Medical Optics Laboratory of Harvard University began to use ruby laser for hair removal. Then ruby laser and Nd: YAG laser were successively used in clinical hair removal treatment, but their parameter design is not ideal. In 1997, Wilman Medical Optics Laboratory began to use a new generation of laser hair removal machine – Lightsheer semiconductor laser hair removal instrument for clinical treatment, and achieved remarkable curative effect. After that, the new intense pulsed light system also began to be used in hair removal treatment. Since then, the optical hair removal technology has been basically mature.

1 principle of laser hair removal

The principle of laser hair removal is still based on the theory of selective photothermal action. Hair follicles and hair stems are rich in melanin, which is distributed between the cells of hair bulb matrix and can also transfer to the structure of hair stem (such as medulla, cortex and hair cuticle). Laser can accurately and selectively depilate with melanin as the target. After absorbing the energy of laser, the temperature of melanin rises sharply, resulting in the destruction of surrounding hair follicle tissue and the removal of hair.

According to the theory of selective photothermal action, as long as the appropriate wavelength, pulse width and energy density are selected, the laser can accurately destroy the hair follicle without causing damage to adjacent tissues. In order to achieve curative effect, it is obvious that the melanin of the hair ball and the bulge above it (the outer root sheath of the hair follicle between the opening of the sebaceous gland and the attachment of the hair follicle of the erector pili, where the hair follicle stem cells are located) must be treated with light. ① Due to the deep part of the hair ball, it is decided to use a light source with long wavelength and deep penetration for treatment. On the other hand, if the wavelength is too short, the melanin of the epidermis will absorb more energy competitively with the melanin of the hair follicle, which is easy to cause epidermal damage. Therefore, while ensuring good absorption of melanin by light wave, the wavelength of hair removal laser is better at 695-1064 nm. ② One solution to achieve high efficiency in hair follicle destruction is obviously to increase the irradiation time of the laser. Theoretically, by lengthening the laser pulse width, the thermal relaxation time close to the hair follicle can improve the curative effect. The longer the pulse width, the less likely the micro structures such as melanosomes in the epidermis will be damaged, while the relatively large structures such as colored hair follicles will be more vulnerable to damage. The diameter of hair follicle is about 200-300 μ m. The thermal relaxation time of hair follicle is 40-100ms. Therefore, the ideal laser pulse width should be between tens of milliseconds and 100 milliseconds. Recent studies have found that for patients with dark skin, using laser with pulse width of more than 100ms not only has better curative effect, but also has less side effects.

The relationship between hair growth cycle and hair removal treatment: ① because laser has no obvious effect on hair in degenerative and quiescent stages, laser can only work after these hairs turn into growth stage, so laser hair removal needs multiple treatments to achieve obvious effect. ② If the proportion of a certain part of hair in the growth period is small, the number of treatments should be increased. On the contrary, the number of treatment can be reduced. ③ Based on different parts of hair, there are different growth cycles, and the interval of each treatment is also different. If the head hair has a relatively short rest period, the interval can be as short as 1 month; The hair rest period of trunk and limbs is relatively long, so the treatment interval is about 2 months. ④ The depth of hair follicles also varies according to the location. If the depth is deep, a longer wavelength laser treatment must be used. On the contrary, if the depth is shallow, a shorter wavelength laser treatment can be used. ⑤ If the hair follicle density of a certain part is too high, the laser energy should be appropriately reduced during treatment.

2 laser hair removal treatment

Indications and contraindications of laser hair removal: laser hair removal is applicable to dark and light hair in all parts, but it is invalid for white hair.

The following are the relative contraindications of laser hair removal:

① History of keloid;

② Have a history of infection or herpes simplex infection in the treatment area;

③ Patients who have used other methods (such as wax removal) for hair removal within 6 weeks;

④ Allergic to hydroquinone or other bleach;

⑤ There was a history of using lsotretinoin (13 CIS retinoic acid) within 6 months.

Preoperative preparation: for patients with type III-V skin with dark complexion, sunlight should be avoided as much as possible before operation. It is best to use sunscreen for 4-6 weeks. Those with pigmentation tendency can be prevented by hydroquinone drugs at the same time. In addition, the skin must be prepared before operation in the treatment area, and the hair must be completely scraped. Its functions include:

① It can reduce the discomfort caused by coking of hair in the treatment area due to absorption of part of laser

② It can reduce the unpleasant smell caused by hair burning.

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