The so-called photosensitive substances are substances that are good at absorbing long-wave ultraviolet light from sunlight. There are often the following three categories: i. Exogenous photosensitive substances that can be exposed to in daily life or in the work environment, such as asphalt, tar, cosmetics, detergents, dyes, food additives, preservatives, anthralin, amidine, halogenated water acyl aniline, bleach, sunflower musk and methyl coumarin. Photosensitive foods are those foods that tend to cause solar dermatitis. Generally speaking, photosensitive foods are digested and absorbed, and the photosensitive substances contained in them will then enter the skin, and if they are exposed to bright light at this time, they will react with sunlight. If exposed to bright light at this time, the skin will react with the sunlight, resulting in redness, swelling and rash on exposed areas of the skin, accompanied by significant itching, burning or stinging sensations. Foods that can produce photoallergic reactions such as: toon, cilantro, celery, rape, mustard, spinach, snow lettuce, amaranth, marjoram, carrot, fennel, buckwheat, lettuce, acacia flower, dragon’s bud, figs, lemon, ashwagandha, purple cloud lettuce, dried fungus, yellow mud snail, prawns, crabs, etc.. If you eat a lot, and sun exposure, you will have vegetable sun rash, fruit sun rash, yellow mud snail sun rash, etc. Third, photosensitive drugs such as chlorpromazine, promethazine, chlorothiazide, hydrochlorothiazide, nalidixic acid, ashwagandha, sulfonamides, tetracyclines, oral hypoglycemic drugs, compound antihypertensive tablets; Chinese herbal medicines containing photosensitive substances such as thornbush, windbreak, dahurica, dahurica, bone marrow and rue.