Ms. Xia: In the hot summer days, many people carry sunscreen with them, but when they use it, some people only apply it once a day, and some people keep applying it to their bodies. How long does it take for sunscreen to be scientific?
Dermatologists: General sunscreen products have their own sunscreen indicators. Women who love to buy cosmetics can find the logo of PA and SOF on the outer packaging of sunscreen. PA indicates the ability of the product to protect against long-wave UV rays, which is the ability to prevent skin tanning. PA+ stands for effectiveness, PA++ stands for quite effective, PA+++ stands for very effective, and the more + sign stands for stronger sun protection.
SPF wax products protect the ability of UVB, which is the ability to prevent skin redness and sunburn. In general, the normal amount of erythema in human skin takes about 20 minutes, that is, when there is no sun protection, the skin will turn red after exposure for 20 minutes in the sun. If the SPF value of sunscreen is 8, use it to apply. Once, in theory, its protection time for the skin is about 20 × 8 = 160 minutes. If you choose a sunscreen with an SPF of 15, you can stay in the sun, ie 300 minutes, and so on. But in fact, the human skin's ability to withstand the ultraviolet rays in the sun varies from person to person, from time to time, and from place to place.
It can be seen that different sunscreens should be used in different environments. Staff and women working indoors can choose SPF10 or PA+ skin care products; people who are more likely to tanning or sensitive to strong light or often work outdoors or Active people can use SPF20, PA++ sunscreen; while walking in the hot sun or swimming on the beach, you should choose SPF30 with good water and sweat resistance, and strong sunscreen with PA+++.
However, do not blindly pursue the SPF value. In fact, the SPF and the sunscreen effect are not proportional to the multiplication. The SPF15 sunscreen can withstand 93% of the UVB, while the SPF34 sunscreen can only resist about 94% of the medium wave. Ultraviolet light. At the same time, products with excessive SPF and PA are either greasy or have poor smoothness to the skin, which can easily clog pores and cause acne or folliculitis.
Since sunscreens require a process to form a protective film, it is generally best to apply sunscreen on the exposed parts of the face, back and upper limbs for 30 minutes before going out, trying to avoid the strongest UV rays in the sun (10 am to 3 pm) Point) go out. It is easy to sweat in summer and it is easy to wash off the sunscreen, so it should be applied every two hours. When in a sunny environment such as a beach, re-apply every 30-90 minutes.