By photosensitive substances, we mean substances that are good at absorbing long-wave ultraviolet light from sunlight. Exogenous photosensitive substances, such as asphalt, tar, cosmetics, detergents, dyes, food additives, preservatives, anthralin, pyridine, halogenated hydantoin, bleach, sunflower musk and methyl coumarin; foods can also produce this photoallergic reaction, such as parsley, cilantro, celery, rape, mustard, spinach, snowcress, amaranth, marjoram, carrot, fennel, buckwheat, lettuce, acacia, lobelia Figs, lemons, grey cabbage, purple cloud lettuce, dried fungus, yellow mud snail, skinny shrimp, crab, etc. If eaten in large quantities and exposed to the sun, vegetable sun rash, fruit sun rash, yellow mud snail sun rash, etc. can occur. Photosensitive drugs: chlorpromazine, promethazine, chlorothiazide, hydrochlorothiazide, nalidixic acid, ashwagandha, sulfonamides, tetracyclines, oral hypoglycemic drugs, compound antihypertensive tablets; Chinese herbal medicines containing photosensitive substances include thorax, windbreak, dahurica, dahurica and rue.