With the gradual advent of summer, sunlight-related skin patients in dermatology outpatient clinics are gradually increasing, and many patients are seen for aggravation after sunlight exposure, and common diseases include solar dermatitis, polymorphic sun rash, summer dermatitis, acne, solar keratosis, lupus erythematosus, chloasma, freckles, etc. Patients are often distressed by this and ask doctors how to protect themselves from the sun, and today, according to the Chinese Journal of Dermatology May 2017, Vol. 50, No. 5 “Skin Sun Protection Expert Consensus (2017)” is briefly introduced as follows for your reference: Knowledge of the spectrum in sunlight Daylight on the earth’s surface has the following three main light sources: visible light, which brings light, accounting for about 52%; infrared light, which makes us feel warm, accounting for about 42%; and ultraviolet light, which is most closely related to sun protection, accounting for about 6%. UVC can destroy skin cell biofilm, damage DNA and kill microorganisms. UVC lamps used for disinfection in hospitals are artificial UVC light sources, and protection should be paid attention to when operating. 2. Medium-wave ultraviolet (UVB): wavelength range 280-320nm, can penetrate the atmosphere, accounting for 5% of the surface UVR, easily blocked by glass. In the summer and afternoon will be particularly strong, can reach the epidermis basal layer, biological effect is strong, 100 times as strong as UVA. The skin reactions often caused are: erythema reaction (i.e. sunburn erythema), delayed darkening, resulting in changes in cell nucleus base structure, and possible induction of photocarcinoma. 3. Long-wave ultraviolet (UVA): wavelength range 320~400nm, accounting for 95% of the surface UV. UVA has strong penetrating ability and can pass through thin clothing, glass, etc., and can pass through the skin epidermis and reach the dermis. The skin reactions often caused are: skin photoaging, immediate darkening, persistent darkening, delayed darkening, induction of cellular reactive oxygen clusters, causing abnormal cell membrane structure, DNA degeneration, destruction of lipids and proteins, leading to precancerous lesions such as solar keratosis. Excessive sun exposure is mainly long-wave UV can lead to skin photoaging (such as skin wrinkles, roughness, pigmentation, relaxation, reduced elasticity, etc.), thus affecting the appearance, while medium-wave UV can induce or exacerbate various light-related skin diseases, such as sunburn, polymorphic sun rash, acne, facial dermatitis, etc. Therefore, it is necessary to reduce excessive sun exposure or even avoid sun exposure, the most important of which is UV protection. For this reason, in 2002, the World Health Organization (WHO) introduced the concept of ultraviolet index (UVI), which is used to indicate the intensity of ultraviolet light in sunlight. The higher the value, the greater the damage to the skin and eyes. This has been used as a parameter for climate forecasting in some areas of China. UVI is generally highest at noon, highest in late spring and summer, and the higher the altitude, the stronger the UVI. Seaside beaches, snow, high-rise building walls or curtain wall glass, car window glass, and hardened surfaces (such as asphalt or concrete roads) all reflect UV light, thus increasing the UVI. For UV characteristics, specific sun protection measures are divided into local sun protection and whole body systemic light protection Local sun protection 1, avoidance sun protection: avoid outdoor activities at noon, late spring and summer, and when you cannot avoid going out you should engage in outdoor activities in the shade of trees and buildings. 2.Shade sun protection: umbrellas, sun hats and clothing and other fabric products can directly block the sun. The higher the density of woven yarn, the darker the color, or with sunscreen coating, the stronger the UV absorption capacity, the better the sunscreen effect. The edge length of the brim is best in 7.5 cm or more, in order to have a better sun protection effect. Local facial skin sensitive patients, sometimes even can not be used externally sunscreen, etc., so it is recommended to wear a black mask, overall type of protection of the face, to avoid buildings or road reflective light. 3, smeared sunscreen: sunscreen is the use of the absorption, reflection or scattering of light to protect the skin from specific UV damage substances. In recent years new sunscreens, natural plant-derived sunscreens and various sunscreen enhancers are coming on the market. The ideal sunscreen cosmetics should have the following characteristics: exact sun protection, sunscreen spectrum covering UVA and UVB; high safety and tolerance, not easy to produce irritation and allergies; products are stable to light, do not make clothing coloring; easy to apply, good breathability. Specific use of product selection: indoor areas that may be subject to UV radiation (such as by the window, exposure to stronger UV light sources, strong fluorescent lamps, mosquito repellent lamps, neon light in entertainment venues, etc.), choose SPF15/PA+ or less; cloudy days or outdoor activities in the shade, choose SPF15 to 25/PA+ to +++; activities in the sun, choose SPF25 to 30+/PA++ to +++; snowy mountains, beaches, plateaus and other environments, or late spring, summer activities under the sun, use SPF50+/PA++++; such as activities involving sweat or underwater work should choose waterproof anti-sweat products. Specific use points: apply the product 30min before going out; general products need to be repeated every 2 to 3 hours; the amount of application to 1 penny size products applied to the whole face is appropriate. Washing: Sunscreen products can be washed off when removed from the light environment; generally wash off with water or cleanser; it is best to apply moisturizing skin care products after cleaning. Systemic photoprotective agents Oral medications or dietary supplements for several weeks to months can protect the skin by combating photo-oxidative damage, repairing cell membranes and DNA, and reducing inflammatory responses, thereby reducing photodamage. Natural food groups include: carotenoids (beta carotene, anthocyanins, lycopene, lutein), polyphenols (flavonoids, resveratrol), lapis lazuli extract, probiotics, selenium, soy isoflavones, chocolate, caffeine, essential fatty acids, etc. Drug classes include: vitamin C/E, niacinamide, non-steroidal anti-inflammatory drugs (acetylsalicylic acid, ibuprofen, indomethacin), antimalarials, glucocorticoids, etc. Newer systemic photoprotective agents: e.g. melanocyte-stimulating hormone analogs, reduce sun exposure damage by darkening the skin. Avoidance of photosensitizers Additional care should be taken to avoid consumption or exposure to photosensitizing substances during prolonged sunlight exposure. Drugs such as tetracyclines, quinolones, estrogens, chlorpheniramine maleate, diphenhydramine, and retinoids. Foods such as ashwagandha, fennel, amaranth, celery, figs, mangoes, pineapples, papaya, etc. Finally, when the photosensitivity reaction occurs due to certain factors, local skin redness, swelling, heat, pain and itching is obvious, local instant cold compress is especially important (common sense of the external application of medicinal water), if necessary, oral antihistamines such as loratadine, cetirizine, etc., if not significantly reduced, promptly go to the hospital or clinic to find a dermatologist for treatment.