Dermatitis is not an independent disease, but a generalized name for skin inflammation, the causes of dermatitis are very many, and its clinical manifestations are also complex and diverse, the factors that cause dermatitis are generally divided into internal and external factors. The internal factors mainly include the following: First, endocrine and metabolic changes, such as menstrual disorders, pregnancy. Second, chronic infection foci, such as chronic cholecystitis, tonsillitis, intestinal parasitosis and so on. Neuropsychiatric factors. Blood circulation disorders, such as varicose veins of the calf. Fifth, genetic factors. And external factors generally include the following can induce or aggravate dermatitis: First, eat some food, such as fish, shrimp and crab, beef and mutton. Second, the living environment, such as cold, hot, dry and so on. Third, inhalants, such as pollen, dust mites and so on. Fourth, animal fur, dander. Fifth, a variety of physical and chemical substances, such as cosmetics, soap, synthetic fibers and so on.