Laser hair removal machine is an instrument that uses the principle of selective thermodynamics to select appropriate power, energy density and light spot according to different characteristics of patients to treat redundant hair.
Laser hair removal can be divided into three categories:
- Laser unhairing without selective damage, such as CO2 laser unhairing, is time-consuming and easy to form scars;
- Photodynamic therapy, such as taking alpha-aminohexanoylpropionic acid orally or topically followed by laser irradiation, seems feasible in theory, but its clinical application is rare;
- Selective photothermal hair removal, namely laser and intense pulsed 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: Laser with a certain wavelength passes through the epidermis, enters the dermis, and is selectively absorbed by melanin particles in hair and hair follicles, resulting in photothermal effect. The heat energy in hair is transmitted to the surroundings, completely destroying “hair roots” such as hair follicles and stem cells, resulting in permanent hair removal. The normal tissue around hair follicles does not contain melanin particles, so it does not absorb this kind of laser, so it is less affected and generally does not cause paralysis marks.
- Thermal relaxation: When the target tissue (melanin in hair follicles) absorbs laser energy, the temperature will definitely rise, and heat conduction must occur to the surrounding tissues. Then the heat conduction of the target to the surrounding tissues is called thermal relaxation.
- Thermal relaxation time: Measure the speed of thermal relaxation. It is the time it takes for the target to reduce its temperature by half (cool down) after absorbing laser heat.
Laser and light source of laser hair removal machine
When using the principle of “selective photopyrolysis” for laser hair removal, the wavelength and pulse width of laser should ensure that the laser hits hair follicles without damaging adjacent tissues. Clinical studies show that the longer the wavelength, the deeper the penetration, the smaller the scattering, but the poorer the absorption of melanin, so the energy will be enhanced, but it cannot harm the epidermis; TRT (thermal relaxation time) with pulse width less than hair follicle is effective, and TRT with pulse width larger than epidermis is safe. The larger the spot size, the deeper the penetration. At the same time, active skin cooling should be used to protect the epidermis and relieve pain. When the wavelength is less than 600nm, the laser is mainly absorbed by hemoglobin and protein, while when the wavelength is greater than 1100nm, the laser is mainly absorbed by water in the body tissue. When the wavelength is in the range of 600nm ~ 1100nm, the light is transparent. Therefore, people usually choose laser with wavelength in the range of 600nm ~ 1100nm for hair removal. The lasers and strong pulsed light sources used for hair removal mainly include long pulsed ruby laser (694nm), long pulsed emerald laser (755nm), semiconductor laser (800nm), long pulsed Nd: YAG laser (l064nm), strong pulsed incoherent broadband light source (590 ~ 1200nm) and so on.
- Long pulse ruby laser
The 694nm ruby laser is strongly absorbed by melanin. This laser has 15%~20% energy to penetrate the entire dermis, and the hair with melanin in the dermis and deep layers can absorb the energy of the laser, causing the hair follicles to overheat and be damaged. The normal tissue around the hair follicle has a very low light absorption rate of 694nm. When the pulse width is constant, selective photothermal damage to the hair follicle can be achieved without damaging the surrounding normal tissue.
- Long pulse alexandrite laser
The 755nm alexandrite laser is very similar to the ruby laser, except that it has a slightly stronger penetrability and a lower melanin absorption rate because it has a slightly longer wavelength.
- Semiconductor laser
The penetration depth of the semiconductor laser system in the skin tissue is more than 5mm, and the range of action can reach the deep dermis and subcutaneous fat tissue. It can effectively penetrate the epidermis to reach the hair follicle tissue of the dermis, thereby destroying hair in any part and depth of the human body. The epidermis absorbs very little laser energy, so it does not produce pigmentation.
- Long pulse Nd: YAG laser
The long-pulse Nd:YAG laser has a wavelength of 1064nm and can penetrate 5-7mm. Due to the low affinity of melanin for the 1064nm laser, exogenous color bases (such as carbon smears) are often used for treatment. The laser spot scans the entire treatment area until the visible carbon particles are removed. The disadvantage is that sometimes the carbon particles cannot reach the hair bulb and affect the treatment effect. For example, sweat glands and sebaceous glands are easily damaged if they are contaminated with carbon particles, and the clinical effect is not ideal. Recently, it has been clinically reported to use a long pulse width laser with a wavelength of 1064nm to remove hair without using carbon smear before surgery. Because epidermal melanosomes are very sensitive to short pulse width (<1ms) lasers, and long pulse width (≤200ms) lasers, high-energy lasers can be used to effectively heat the inner and outer hair root sheaths and hair growth areas without affecting Epidermal melanosomes, so it can be safely used for the treatment of black skin.
- Strong pulsed light
High-intensity pulsed light is not a laser light source, but a non-continuous, multi-wavelength combination light source. Its wavelength is between 550 and 1200 nm and can penetrate 1.3 mm. The treatment parameters can be adjusted according to skin color or hair color. Theoretically, the broad-spectrum wavelength light source system increases the absorption of light by non-target targets, and therefore also increases the adverse reactions.
Features of laser hair removal equipment
- Long-pulse ruby laser: The wavelength is 694m, which is the shortest wavelength among clinical hair removal lasers (it is not commonly used at present). The wavelength is short and the penetration depth is limited. It is suitable for patients with light skin and dark hair, but it has limited effect on the deeper parts of the hair follicles. With strong melanin selective absorption performance, energy is not only absorbed by melanin in hair follicles, but also by melanin in epidermis, which is easy to cause epidermal damage.
- Long-pulse alexandrite laser: The wavelength is 755nm and the penetration depth is deeper than that of ruby laser. It is a common hair removal laser in clinic. It has good treatment effect, relatively few and short-lived adverse reactions, such as erythema, skin pigmentation, folliculitis, etc. , It is mainly seen in patients with darker skin or cold compresses on the treated area after the hair removal operation.
- Semiconductor laser: The wavelength is 800nm, which is one of the ideal laser hair removal systems with the most clinical applications. The penetration depth is deeper than the ruby laser and emerald laser, and the hair follicle melanin absorbs photons at 800 nm relatively strongly, which can effectively destroy the hair follicle. Compared with the red and alexandrite lasers, the epidermal melanin absorbs less energy from the semiconductor 800nm laser and has relatively few adverse reactions. Semiconductor laser has low cost, high reliability and small size.
- Long pulse laser: The wavelength is 1064nm, and the penetration is deeper, so it is especially suitable for patients with darker skin. The absorption of melanin at this wavelength is reduced, the hair follicles cannot be completely destroyed, and the hair will continue to grow. At the same time, the melanocytes of the hair follicles are destroyed, and the melanin production is reduced, causing the part of the hair that grows to become white. Therefore, treatment requires high energy to destroy the hair follicles. .
- High-intensity pulsed light: high-intensity pulsed light is not a laser light source, but a non-continuous, multi-wavelength combination light source, with a wavelength of 550-1200m. Its cooling system is good, the probability of skin trauma is low, and the side effects are small. . It takes multiple treatments to achieve the hair removal effect, and its hair removal effect is slightly inferior to that of laser.
Factors that affect the effect of hair removal
- The choice of laser type (ie wavelength): When choosing what wavelength of hair removal laser, two factors need to be considered, one is the penetration depth of the laser; the other is the selectivity of target absorption. Because the hair bulb is deeper, it is decided to use a laser light source with longer wavelength and deeper penetration for treatment. If the laser cannot penetrate or penetrate shallowly and cannot reach the hair growth area, it will be difficult to see the effect. Generally, the penetration depth of the laser increases with the increase of the wavelength. Studies have shown that the ideal wavelength for destroying hair follicles is about 700nm. Another way to increase the penetration depth of the laser is to increase the light spot, which can reduce the loss of the laser in the tissue and make the laser penetrate deeper in the skin. In addition, the size of the spot also affects the speed of treatment.
- Determination of parameters: Laser hair removal is affected by various parameters such as wavelength, spot, pulse width and energy, but the ideal value of each parameter is not yet known. According to the principle of selective photothermal action, while ensuring the selective absorption of melanin by light waves, its wavelength should be as long as possible. Theoretically, by lengthening the laser pulse width to make it close to the thermal relaxation time of the hair follicle, the therapeutic effect can be improved. Because the longer the pulse width, the less likely it is that the tiny structures in the epidermis, such as the melanosomes, will be damaged, while the relatively large structures, such as the melanosomes in the hair follicle, will be more susceptible to damage. It is generally believed that the ideal hair removal laser pulse width should be between the thermal relaxation time of the epidermis (3-10ms) and the thermal relaxation time of the hair follicle (40-100ms).
Indications, contraindications, complications
- Indications: It is suitable for dark and light-colored hair in all parts, but it is not effective for white hair.
- Contraindications: Scar constitution, infected lesions or history of herpes simplex in the treatment area, patients who have used other methods (waxing, electrolyte, etc.) to remove hair within 6 weeks, are allergic to hydroquinone or other bleaching agents, or within 6 months Those with a history of using 13-cis Tretinoin.
- Complications: The common complications are local erythema and follicular edema after surgery, which may resolve spontaneously after a few hours. Rare complications are local scabs, purpura, blisters, hyperpigmentation or hypopigmentation, and increased sebum secretion.
The technical operation of laser hair removal seems very simple, but the experience of the operator affects the treatment effect. Although the operation of each type of machine will be different, it should generally include the following steps:
- Investigate the medical history, check the recipient, analyze the skin type, and check the hair condition.
- Turn on the power to warm up the machine.
- Preparation of the treatment area: hair should be shaved before treatment, because visible hair will damage the epidermis due to high heat caused by laser burning, and can also cause irreversible damage to the laser guide head and cause unpleasant odors, but machinery cannot be used. Epilation or wax depilation. In addition, the local area should be cleaned to remove grease and dirt.
- Set the treatment parameters and conduct trial treatments.
- Get the best parameters and complete the entire treatment.
- Check the response after treatment and explain the relevant precautions.
Precautions for use
- During the treatment, both the physician and the recipient should wear laser protective glasses to prevent the eyes from being damaged by the laser.
- The light spots should not overlap too much, repeated irradiation will aggravate skin damage, and too wide spacing will affect the treatment effect.
- When semiconductor laser hair removal, such as using cooling hand tools or hair removal under strong pulsed light, apply a certain pressure to the hand tools during the treatment, so that the hand tools can maintain better contact with the skin, and it can also drive away local blood and reduce Oxyhemoglobin absorbs laser energy.