1.Application should be sufficient amount. Internationally, when testing the SPF and FPA values of sunscreen cosmetics, it is usually required to apply 2mg of sunscreen cosmetics per square centimeter. But consumers in daily use, often the amount of sunscreen cosmetics applied, can only reach about 0.5mg per square centimeter, just a quarter of the test, then, of course, the corresponding protection against ultraviolet rays can not reach the value of protection indicated by the product. 2, it is best to apply more than 2 times within half an hour before going out, mainly refers to the chemical sunscreen. 3, chemical sunscreen in a number of photothermal conversion, will eventually decay failure, so if you continue to be in the outdoor activities, generally should be 2 to 4 hours to replenish the rub once, so as to maintain effective sunscreen effect. 4, water or sweat should be careful to choose the following signs of the product: Waterproof: waterproof, refers to the sunscreen efficacy can be maintained in water 80 minutes. Water resistant: water resistant, means the sunscreen efficacy can be maintained in the water for 40 minutes. Sweat resistant: sweat resistant, means the sunscreen efficacy can be maintained in the water for 30 minutes.