With the warmth of spring, the temperature is rising and UV radiation is becoming more intense, so more and more people are going out for excursions. The former is a phototoxic reaction, which can happen to everyone after severe exposure to the sun, manifesting as skin erythema, burning sensation, and even blistering in severe cases, such as the performance of boiling water burns; while the latter is only seen in a small number of people, caused by allergic reactions to UV-induced products, papules, blisters, patches, etc., in the exposed areas, itching and tingling sensation. Itching and tingling sensation. In this regard, it is important to remind people to protect themselves from the sun when they go out. UVB causes skin reddening and UVA causes skin aging. In addition to visible light, there is about 1% of ultraviolet (UV) light in sunlight. According to the length of the wavelength, it can be divided into long-wave ultraviolet (UVA), medium-wave ultraviolet (UVB), short-wave ultraviolet (UVC), the shorter the wavelength, the greater the harm to the skin. The shortest wavelength UVC is usually absorbed by the ozone layer and rarely radiates to the ground, while UVA and UVB are the most important components that cause skin damage. UVA easily damages the dermis of the skin, destroying the fibrous tissue, thus making the skin tend to age and form wrinkles; UVB easily damages the epidermis, causing skin darkening, redness, inflammation, pigmentation and even skin cancer. In addition to direct sunlight, scattered UVB rays reflected from the sun through the atmosphere, sea and beaches can also cause and aggravate skin damage, so you should pay more attention to sun protection when you go to the water and beach. The U.S. Food and Drug Administration (FDA) recommends the use of photoprotection measures including avoiding solar radiation during the peak UV radiation period, wearing clothing with photoprotection, wearing broad-brimmed hats and sunglasses, and using broad-spectrum sunscreens, among which the correct use of broad-spectrum, stable sunscreens is most important. How to choose sunscreen? UVA penetrates the skin more deeply than UVB, and its energy is 30-100 times higher than UVB, so the new sunscreen products on the market are almost all broad-spectrum protection against UVA and UVB at the same time. UVB protection effect is measured by SPF (sun protection factor) value, assuming that the intensity of UVB is a constant value in a certain period of time, a person without any sun protection measures exposed to the sun after m hours of skin will turn red, when he uses SPF value n sunscreen products, the amount of 2mg/cm2, in n × m hours of time before his skin turns red. In general, SPF10 or so can protect the sun for 2 hours, SPF20 or so for 4 hours, SPF30-40 is more than 5-6 hours. The level of UVA protection effect is measured by PA (Protection of UVA) value, which is divided into three levels: PA+ means it can delay the skin tanning time by 2-4 times, PA++ means it can delay the time by 4-8 times, and PA+++ means it can delay more than 8 times. How to use sunscreens? If it is a long time outdoor activity, you should choose about SPF 30, and for people who are indoor for a long time, SPF 15 is enough. This is because the larger the SPF, the less permeable it is, which will hinder the normal secretion and breathing of the skin. Sunscreen generally takes about 20 minutes to work, and the sunscreen ability decreases as the skin is exposed to time, so it must be applied 20 minutes before going out, and then replenished before going out, the effect is good; in the use of dose, each time at least l-2mL amount, and wipe every 2 hours. For water sports players, they require higher SPF and PA values, and need their high fat solubility to be able to resist water immersion for a longer period of time. The radiation at the seaside is nearly 20 times higher than under normal circumstances, and professional sunscreen should be used for swimming at the beach. Photosensitive foods also need to be avoided In addition to sunscreens, attention should be paid to the use of comprehensive preventive measures, such as reducing the intake of photosensitive foods such as celery, parsley, citrus, lemon, mango, pineapple, etc., because these foods can aggravate skin photodamage.