Did you use sunscreen right

Sunscreen: sunscreen containing chemicals that can filter ultraviolet rays and protect the skin should be used before direct exposure to strong sunlight. In the past, sunscreens can only filter UVB, but now many new sunscreens also have the broad-spectrum sunscreen function of effectively filtering UVA. Sunscreen contains substances that can absorb ultraviolet rays, such as p-aminobenzoic acid (PABA) and benzophenone. Since PABA cannot adhere firmly to the skin immediately, when using a sunscreen containing PABA, it must be applied for 30 minutes before it can be exposed to the sun or into water. PABA may irritate the skin and cause contact dermatitis in some people. Many sunscreens contain PABA and benzophenone or other substances. These composite preparations can block ultraviolet rays with a wider wavelength. Many sunscreens claim to be waterproof or water-resistant, but nevertheless, most of these products still need to be reapplied after swimming or sweating. There is also a sunscreen called sunscreen, which contains substances with physical barrier function such as zinc oxide or titanium dioxide. These viscous white ointments block almost all sunlight and can be used in local sensitive areas, such as nose and lips. Some cosmetics contain zinc oxide or titanium dioxide. In the recent new sunscreen, it has the characteristics of thinner texture and more natural color. It can be used in combination with some other traditional chemical sunscreen substances to better improve the sunscreen performance. In the United States, the solar protection index (SPF) is used to evaluate the performance of sunscreen. The higher the SPF value, the better the protection effect. A sunscreen index of 2-12 provides minimum protection, an index of 13-29 provides medium protection, and an index of 30 and above provides maximum protection. However, SPF value can only evaluate the protection performance against UVB, and there is no rating standard for UVA.