UV damage to human skin does have seasonal differences: spring long-wave ultraviolet UVA is more than 10 times that of winter, and spring UVA energy for the first of the four seasons; a lot of clinical data also confirmed photosensitive skin disease in the spring there is a relatively high incidence, which is related to the exposure of UVA; the following figure can be seen UVA directly to the dermis, and UVB is mainly absorbed in the epidermis. In that case, it’s time to protect against it. How? First of all, clothing is one of the most effective protection, textile raw material fiber density and interweaving uniformity is the key; but the beauty of the clothes have become thinner and shorter, the skin is unknowingly overexposed, protection of the head and face can come to a classic French wide-brimmed hat, in fact, it is what we farmers uncle wore; and then there are light protectants, that is, sunscreen. About sunscreen, there are some issues that have to be said. One is SPF, PPD index on behalf of what SPF is a small piece of the skin surface protected by sunscreen products caused by the minimum sun spot required UV energy and no protection of the skin caused by the same erythema required UV energy ratio; PPD is caused by the product protection of the minimum skin pigmentation required energy and the unprotected and the same pigmentation of the ratio of energy. The former for UVB, the latter for UVA. Since it is clear that these two indices are a ratio, it is not difficult to understand: you do not apply the product, in the sun for 1 minute will be red, if you choose a SPF 30 sunscreen today, after applying, it is 1 minute x 30, 30 minutes will not appear skin redness, and once beyond 30 minutes, the sunscreen is no longer have the effect of sun protection. Therefore, in the need for prolonged exposure to the sun, must be timed to repeatedly apply sunscreen, in order to play the efficacy. The second point, you must know, both parameters are in the human back skin to complete the test, in accordance with international standards, human skin sunscreen use is 2mg/cm2, the thickness of the thickness of the wall with your brush compared to the thickness of the difference! A survey shows that most people are accustomed to using a dose of only about 0.75mg/cm2, in fact, is far from being able to achieve the protective effect promised on the product packaging. The third point, sunscreen actually prevent what? In the short term, it is to prevent sunburn, edema and erythema, tingling, secondary flaking; in the medium term, it is to prevent sun spots on your face, lighten freckles, chloasma, post-inflammatory pigmentation spots, and its effect may be better than the whitening cream you use every night; in the long term, it is to prevent skin tumors, and a lot of cross sectional investigations in Europe and the United States have shown that the crowd’s understanding of the knowledge of sunlight protection and its application are closely related to the occurrence of skin tumors. Many cross-sectional surveys in Europe and America show that the understanding and application of sunlight protection knowledge is closely related to the occurrence of skin tumors, and there will be a good preventive effect once scientific education and behavioral intervention are carried out.