The wavelength of ultraviolet light in sunlight is mainly 200-400nm, including short-wave ultraviolet UVC (wavelength 200-280nm), medium-wave ultraviolet UVB (wavelength 280-320nm) and wavelength ultraviolet UVA (wavelength 320-400nm), the longer the wavelength of ultraviolet light, the stronger the penetration, but also the more difficult to protect. Most of the UVC is absorbed by the ozone layer when it passes through the atmosphere, and there is very little left when it reaches the earth’s surface, so it does not pose a danger to human skin (UV disinfection lamps emit high-intensity UVC, so special attention should be paid to protection). UVB is mostly absorbed by the epidermis, mainly causing skin tanning, sunburn and cancer; UVA can penetrate into the middle of the dermis, mainly causing wrinkles, skin elasticity reduction and other skin aging changes. Physical sunscreen and chemical sunscreen Physical sunscreen ingredients, such as titanium dioxide and zinc oxide, reduce the amount of UV rays entering the skin through reflection and scattering of UV rays, because they cover the skin surface, are not absorbed and do not undergo chemical reactions, so they are less irritating to the skin and rarely have allergies. However, the weakness is that it is often thicker, greasy, not breathable, easily whitened, less natural, and has a poorer feeling of use. In recent years, physical sunscreens such as titanium dioxide and zinc oxide have been made into particles less than 0.2 microns in diameter, which are more delicate and lighter in texture and better breathability. Chemical sunscreen ingredients such as octyl methoxycinnamate (OMC), octyl-salicylic acid (OCS), p-aminobenzoic acid (PABA) and benzophenone-3 (Oxybenzone), etc., is through a chemical reaction with ultraviolet light, ultraviolet light will be absorbed, transformed into harmless heat and reduce the transmission of ultraviolet light. Since the chemical reaction occurs on the skin, irritation or allergy may occur. SPF The Sun Protection Factor (SPF) is the only international standard for measuring the ability of sunscreens to filter UV rays and indicates the level of sun protection that sunscreens can provide. It is based on the minimum erythema dose to the skin (MED), which is the minimum dose of UV exposure needed to produce well-defined, detectable skin erythema. SPF of sunscreen = minimum erythema amount (after using sunscreen) / minimum erythema amount (before using sunscreen). Generally speaking, the higher the SPF of a sunscreen, the greater the protection it possesses. The average yellow skin can withstand bright light for 15 minutes without being burned, so theoretically using SPF 15 UV protection products can withstand about 225 minutes of UV exposure, when the exposure time exceeds the effective sun protection time should be promptly replenished and applied. Is it better to choose a sunscreen with a higher SPF? In fact, not, according to the skin in the specific environment to choose. To the Oriental skin type, daily maintenance as long as the use of SPF15 sunscreen, do not need too high sun protection factor, only in the long sun or outdoor sports, only need to use SPF30 or even higher sunscreen, to resist the damage of UV rays on the skin. If you pursue a high sun protection factor, it will instead cause an unnecessary burden on your skin. It should be noted that the SPF value is mainly for the UVB protection effect, the strength of the UVA protection ability to PA value after the “+” number to indicate, PA + means effective, PA + + + means quite effective, PA + + + means very effective. Waterproof performance For outdoor sports, travel enthusiasts, sweat, seawater, swimming pool water, etc. are the problems we face when using sunscreen, so the waterproof performance of the sunscreen is also very important. Even waterproof sunscreen is actually only “water-resistant”, although it can maintain a certain degree of stability in the efficacy of water, but after sweating, wiping sweat and swimming, or should promptly replenish the sunscreen. Sunscreen use of tips Use the appropriate time: should be 20 minutes before leaving home to apply sunscreen. When you are outdoors or in the sun for a long time, you need to reapply it in time. In general, you should reapply it once in about 2 hours. If you feel that ordinary sunscreen is not convenient, there are now many powder sunscreen products to choose from. The amount used should be sufficient: usually sunscreen is applied to the skin at 2 mg per square centimeter in order to achieve the proper sunscreen effect. However, SPF cannot be cumulative. Applying two layers of SPF 10 sunscreen does not achieve the protective effect of SPF 20, so there is no need to repeatedly apply multiple layers. Use parts to be comprehensive: need to pay attention to apply to all exposure parts, especially pay attention to the neck, chin and ears, to avoid uneven application of a large flower face. Different sunscreen do not mix: the composition of sunscreen brands is inconsistent, mixed with the ingredients may cause mutual interference or reaction, resulting in the instability of the sunscreen itself, reducing the effectiveness of the sunscreen, and even cause skin allergies. Thirty-six strategies, “hide” for the top plan: try to avoid going out in the strongest hours of sunlight (10:00 a.m. – 2:00 p.m.), try to stay in the shade, while making good use of a variety of auxiliary supplies, such as umbrellas, hats, long-sleeved clothing, sunglasses, etc., together to resist UV invasion. You can eat “sunscreen” sun exposure will cause the increase of oxygen free radicals and damage to the skin, excessive production of pigment and deposition, so appropriate food can be antioxidants to pigment can also have a certain protective effect on sun exposure. Foods high in vitamin C (such as kiwis, tomatoes, saints, oranges and guavas), carotenoids (such as carrots), beans, nuts, green tea, etc. can be antioxidants and inhibit photodamage and pigmentation of the skin.