防晒知识（Sunscreen knowledge）.doc

防晒知识（Sunscreen knowledge） Ultraviolet light divides three kinds of light waves - UVA, UVB, and UVC. Heres the first science. What are UVA, UVB and UVC?. First of all, because the UVC cannot pass through the atmosphere, there is no UVC on the surface of the earth. There is no discussion about the necessity. We mainly talk about the familiar UVA and UVB. UVA is ultraviolet light that can penetrate human skin through windows, glass and clouds. UVB is outdoor ultraviolet light, which is injected directly into the skin during outdoor activities. UVA and UVB, which are not absorbed by the ozone layer, will shine on the earths surface, causing damage to our skin. Of these, UVA is the cause of pigmentation and wrinkles in the skin due to sun aging. UVB causes immediate sunburn, redness and blisters. In summer, the content of UVB in the sun is the highest in the four seasons. People who work outdoors often should use SPF sunscreen for 30 to 40, and it is enough for office staff to choose products with a SPF value of 18. Winter, the content of UVB is the lowest in four seasons, the sunscreen SPF value should not be too high. The amount of UVA in the sun varies little with season, so sunscreen used throughout the year should contain a protective component of UVA. As technology advances, sunscreen products, both UVA and UVB, have been developed that prevent sunburn and prevent tanning. Therefore, the bottle of treasure Thailand beach drying for a whole week, not black, that is because sunscreen work done enough Oh ~! UVA is the wavelength range 320 ~ 400 nm wavelength, has a strong penetration, can penetrate the glass, even 9 feet of water; and the seasons of the year, regardless of Yinqing, there are. More than 95% of the daily skin exposure is UVA, so it does most damage to the skin. UVA attacks the dermis through the epidermis, resulting in severe damage to collagen and elastin in the skin, and the ability of the dermis to protect itself is poor, and a small amount of UVA ca