Many skin problems are related to sun exposure: such as discoloration, wrinkles, skin aging, sagging, and red blood cells. One of the culprits is the sun’s ultraviolet (UV) rays, which cause sunburn in the medium wave (UVB) and aging in the long wave (UVA). UV damage to the skin is cumulative, which means that every time you receive unprotected sun exposure, you are one step closer to aging. UVA is present in all seasons and in all types of weather, so sun protection is not seasonal in terms of preventing photoaging. uVA can penetrate glass and enter the room, so sun protection is also needed indoors and in closed cars. In addition to applying sunscreen, you can choose physical shade when the sun is very strong, such as wearing a sun hat, playing a sunshade, and wearing clothes with long sleeves and long pants. In addition to the face, pay attention to sun protection for the neck and hands. Because the face, neck and hands are part of the year-round exposure to UV rays, very easy to form photoaging, must not be ignored. Sun protection around the eyes and lips is also important, and you need to choose a special sunscreen. Among all cosmetic products, it seems that only sunscreen carries a unique mark called sun protection factor. When buying a sunscreen, the first thing you need to pay attention to is the sun protection factor. I believe many people have this doubt: is the higher the sun protection factor, the better it is? Then it is good to know what is the sun protection factor? 1, SPF (sunprotectionfactor), called the sun protection factor. SPF is the earliest proposed sun protection factor, is the protection factor for UVB. We all know that when exposed to sunlight without any protection, the skin will be reddened and in severe cases, sunburned. The main cause of this damage is UVB. here there is a concept of the minimum amount of erythema, which refers to the minimum amount of UVB for which the skin is erythematized, and the minimum amount of UVB for which the skin is erythematized will increase after the skin rubs sunscreen. It can also be roughly understood as assuming that the skin in the absence of any protection, exposure to the sun for 20 minutes after the skin will have red spots, that after applying SPF15 sunscreen products, to be exposed to the sun for 20 * 15 = 300 minutes before the same degree of red spots appear. 2, PA (protectionfactorofUVA, also known as PFA) is the protection factor for UVA. People gradually found that although the sun’s UVA does not cause sunburn reaction to the skin like UVB, but can unknowingly make the skin aging, discoloration and wrinkles, so protection against UVA is equally important. There is no specific index, only divided into +, + + +, + + + three levels, PA + about 4 hours, PA + + + about 8 hours, PA + + + + is super protection. Experiments have shown that the sun protection factor of 30 products used correctly can provide adequate protection for the skin, so our country in 2005 to limit the sunscreen products SPF value, the product is no longer allowed to indicate the SPF30 coefficient, SPF more than 30 all to SPF30 +, to avoid misleading consumers. Tips: It should be noted that the sun protection factor is measured in the laboratory in strict accordance with the use of the requirements and thickness of the application. The actual use, the average person is difficult to apply sunscreen to sufficient thickness, but also because of sweating, face wipe, etc. caused by the loss, if not timely replenishment of the rub, it will not be able to achieve the protection provided by the marked value. The level of sun protection factor is just a reference and not completely dependent on it. Some people choose a high sun protection factor products, think you can rest easy, the results found or tanned, and then think that the product is not good, in fact, may be because not applied with enough thickness or not timely replenishment rub, so that the correct use of sunscreen is far more important than the factor.