Laser damage to the skin When the skin is irradiated by laser, when the energy density (or power density) of the laser is large enough, skin damage can be caused. The damage is mainly manifested as skin redness, blisters, gasification, scorching, burning, etc. The degree of laser damage to the skin is related to the power density and wavelength of the laser, the depth of the skin color, the moisture contained in the tissue, and the thickness of the stratum corneum.

The greater the power density (or energy density) of the laser irradiating the skin, the greater the damage to the skin. The mechanism of laser damage to the skin is mainly caused by the thermal effect of the laser. The laser is incident on the skin, and the skin heats up as the energy absorbed by the laser increases. As the temperature increases, the skin there will be damaged to varying degrees. Especially infrared lasers, such as CO2 lasers, the skin has a high absorption rate of infrared lasers of this wavelength (10 600nm), but the transmittance is very low, so the skin strongly absorbs this kind of laser, which makes the local temperature rise of the skin very high. , when the temperature rises to 47 °C, the skin will blister within a few seconds, and when it reaches 55 to 60 °C, the enzyme will lose its catalytic activity, the protein molecules will be coagulated and denatured, and the DNA will be inactivated. High, the skin is vaporized, carbonized and burned, so great attention should be paid to the safe use of CO2 lasers.

The degree of laser damage to the skin is determined by the transmittance and absorption rate of the skin to the laser. For the same skin, the transmittance and absorptivity of the laser are determined by the wavelength of the laser. If the transmittance is high, it mainly causes damage to the subcutaneous tissue, and the damage to the skin itself is light; if the absorption rate is high, it mainly damages the skin, and the laser penetrates into the subcutaneous surface very shallowly. The skin has a high transmittance of visible laser light, so when there is no damage on the skin surface, it may cause damage inside the skin; the skin has a high laser absorption rate for ultraviolet light and infrared light, so these two types of lasers are the main damage to the skin. laser band. The effect of infrared lasers on the skin is thermal burns. When this type of laser irradiates the skin, it can dilate the capillaries and make the skin red and hot when the power is relatively small. As the laser power density increases, the degree of thermal burn also increases. The effect of UV laser on the skin is mainly photochemical. When the ultraviolet laser irradiates the skin, it can cause skin erythema, aging, and even cancer in excess. Among the ultraviolet lasers, the ultraviolet light with a wavelength of 270-290 nm is the most harmful to the skin. When the wavelength is larger or smaller than 270-290nm, the degree of harm is relatively reduced. Table 3-15-3 lists various symptoms that occur when the human eye and skin are irradiated with excessive laser light of different wavelengths.

The darker the skin tone, the more melanin particles are contained in the skin cells, and the pigment particles can convert laser energy of various wavelengths into heat energy. The heat energy is diffused around, causing the skin to heat up, causing protein coagulation and denaturation, cell and tissue damage and death. The more melanin particles in the skin, the more cells are destroyed and die after being irradiated by laser light. This shows that when the same intensity of laser is used on the skin, the darker the skin, the heavier the damage.