The so-called photosensitive substances are those that are good at absorbing long-wave ultraviolet light from sunlight. It is divided into endogenous (such as porphyrins) and exogenous (such as certain foods, certain drugs, etc.). Foods with photosensitivity are: parsley, celery, rape, spinach, ash, snow lettuce, lettuce, carrots, toon, fennel, horsetail, buckwheat, figs, acacia, lemon, dried fungus, yellow mud snail, shrimp, crab, etc. If eaten in large quantities and sun exposure, vegetable sun rash, fruit sun rash, yellow mud snail sun rash will occur. Photosensitive drugs include: chlorpromazine, isopromazine, chlorothiazide, hydrochlorothiazide, tetracyclines, norfloxacin (haloperidol), lomefloxacin, sparfloxacin, enoxacin, sulfonamides, ashwagandha, oral hypoglycemic drugs, compound hypotensive tablets, nalidixic acid, etc.; Chinese herbal medicines containing photosensitive substances include: antiphlogistic, thornbush, dockwood, dahurica, rue, bone fungus, etc. After taking these drugs orally, attention should be paid to avoid light, otherwise it may cause photosensitivity reactions. Other: food additives, preservatives, bleaching agents, cleaning agents, cosmetics, dyes, anthralin, tar, asphalt, amidine, halogenated water acyl aniline, sunflower musk and methyl coumarin, etc.