When it comes to sun protection, let’s list a few skin problems related to sun protection: pigmentation, wrinkles, aging, sagging and red blood. These are all caused by the accumulation of long-term damage to the skin from UV rays when people do not pay attention to sun protection. In other words, every time you receive unprotected sun exposure, you are one step closer to aging and may even lead to the occurrence of some skin malignancies. Therefore, we can see the importance of paying attention to sun protection in general. Among all cosmetics, it seems that only sunscreen comes with a special mark called sun protection factor. You must have a lot of doubts, for example, what is the sun protection factor? Is the higher the sun protection factor the better? Sunscreen usually how to choose? 1, SPF (Sun Protection Factor) – sun protection factor, it is for UVB protection factor. As we mentioned earlier, when exposed to sunlight without any protection, the skin will be reddened and in severe cases even sunburned. The main cause of this damage is UVB. here leads to the concept of a minimum amount of erythema, which is the minimum amount of UVB for which the skin is erythematous (MED1) and the minimum amount of UVB for which the skin is erythematous (MED2) after the skin is coated with sunscreen, SPF = MED1/MED2. in layman’s terms, it can also be understood as assuming that the skin is exposed without any protection After 20 minutes of sunlight, there will be erythema, and after applying SPF 15 sunscreen, it will take 20 x 15 = 300 minutes of sunlight exposure before the same degree of erythema will appear. This also explains that sunscreen is not a one-off, need to be repeated after a certain amount of time or sweat to achieve a lasting sunscreen effect. 2, PA (Protection Factor of UVA). Research has found that although UVA is not like UVB that causes sunburn reactions on the skin, but unknowingly makes the skin aging, discoloration and wrinkles, so protection against UVA is equally important. There are currently three levels of UVA, + (2-4 times), +++ (4-8 times), and ++++ (8 times or more). We need to note that the sun protection factor is measured in the laboratory in strict accordance with the requirements of use and thickness applied with, the actual use, the average person is difficult to apply sunscreen to sufficient thickness, and will cause loss because of sweat, wipe the face, etc., if you can not timely replenish the wipe, 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 you can’t rely on it completely. Some people choose a high sun protection factor products, think you can rest easy, the results found or tanned, thought it was a product treatment is not good, in fact, may be because not coated with enough thickness or not timely replenishment rub, so that the correct use of sunscreen is far more useful than the coefficient. Currently available in the domestic market sunscreen, it is recommended that you use the sun protection factor for (SPF30+, PA++) type. In addition, if you have photosensitive diseases (such as sun-sensitive dermatitis, photosensitive connective tissue disease, etc.), the application of sunscreen can play a certain effect, but the most important thing is to avoid direct sun exposure, if it is really difficult to avoid, it is recommended that on the basis of the application of sunscreen and then wear long-sleeved shirt, wear a broad-brimmed hat, play umbrella, etc. to avoid sun exposure.