Into the hot summer, sunscreen has become an urgent topic. Sunlight in the ultraviolet light is divided into UVA (long-wave ultraviolet), UVB (medium-wave ultraviolet), UVC (short-wave ultraviolet), which has a greater impact on the skin of the UVB and UVA, UVB mainly cause acute skin light damage, such as sunburn, and UVA can reach the dermis, resulting in skin aging. So sunscreen not only to prevent UVB, more importantly, to prevent UVA. First, on the sunscreen logo SPF (Sun Protection Factor) is to show the sunscreen effect to prevent UVB damage to the value. It is calculated as follows: SPF = minimum erythema (after sunscreen) / minimum erythema (without sunscreen). Assuming that the intensity of ultraviolet rays does not change with time, a without any sunscreen measures if stay in the sun after 20 minutes the skin will turn red, when using sunscreens with SPF 15, it is said that it can be prolonged by 15 times, that is, it will not be reddened until after 300 minutes. PA is the “UVA prevention effect measurement method standard” announced by the Japan Cosmetic Industry Association (JCIA) in 1996, and the test standard is the index of persistent melanin deposition (PPD) of the skin after 2-4 hours of sunlight exposure. Japan Cosmetic Industry Federation will be divided into four levels of PA protection, respectively, PA +, PA + + +, PA + + + +, PA ++++, “+” the more, the better the effect of anti-UVA, the longer the effective protection time. Second, the three main features of the choice of sunscreen products AAD American Academy of Dermatology suggests that consumers choose the three main features of sunscreen products: 1. sun protection index is not less than SPF30; 2. the use of broad-spectrum sunscreen products: can protect against both UVB and UVA two kinds of ultraviolet damage; 3. water-resistant: can be maintained to a certain extent after exposure to water after the efficacy of the stability of the maintenance of 40 to 80 minutes, but in the swim After swimming and sweating, it is still necessary to supplement the application of sunscreen products in a timely manner. Third, the correct way to use sunscreen products 1. 20 minutes after applying sunscreen before going out. Because sunscreen needs to be applied for a period of time before it is absorbed by the skin and comes into play; 2. Apply sunscreen every 2 to 3 hours; 3. When you go out in sunny weather, it is best to wear a hat, sunglasses, or a sunshade.