Epidemiological characteristics vary according to the region, race, population, level of industrialization and its economic development, and diagnostic criteria, and there is no exact prevalence yet. The etiology and pathogenesis: I. Etiology The etiology is complex and unclear, but is generally recognized to be related to genetic factors, immune factors and environmental factors. （The incidence of atopic dermatitis in children of mothers with atopic dermatitis is 25% in the first 3 months of life and more than 50% within 2 years of age; the incidence of atopic dermatitis in children of both parents is as high as 79%. (B) Immunological abnormalities Recent research data indicate that the development of atopic dermatitis is related to autoimmunity, and IgE auto-reactivity can have a pathogenic role in the development of atopic dermatitis. （The most prominent environmental factors for AD in children are allergens, including inhalation, ingestion, exposure, additives and other factors. 1, inhalation allergens: common are pollen, dust mites, mold, animal hair and dander, especially when pollen and dust mites. Dust mites are suitable for living in a warm, humid environment, attached to dusty surfaces and various textiles, such as pillows, bedding, mattresses, carpets, toys, upholstered furniture (such as fabric sofas, etc.) above, to shed skin lesions for food. Through cleaning and exposure, the condition of AD in children improved significantly. 2. Ingested allergens: There are many kinds of food allergens, and food allergy and food intolerance have a considerable incidence in children with AD again. According to European and American data, the incidence of food allergy in children under 9 years old is about 7.8%, and preschool AD, especially infantile AD, is more likely to have food allergy. Eggs, milk, soy, nuts, wheat, fish, and shellfish are the main food allergens. Food allergies in children can be alleviated. Like adaptation to the environment, it is a gradual, ongoing adaptation process that also varies from person to person, with the length varying from a short period of about a year to a long period of up to 10 years or more. Milk allergy can be relieved or tolerated by infants around 1 year old; about 80% of infants with cereal allergy can be tolerated around 3 years old; while egg allergy remission or tolerance appears later and can last 2-3 years; peanuts, nuts, fish and shellfish allergic reactions will last longer. 3, other: there are more uncertainties in environmental factors, which must be closely observed over a long period of time to determine whether there is an allergic reaction. Such as contact with woolen and chemical fiber clothing, toys and animals, playing with sand and water, passive smoking, poor washing and hygiene habits, improper care, indoor humidity, season, especially the dry winter season, etc. can be allergens related to the onset of the disease. 4, microorganisms: bacteria, fungi, viruses and other microorganisms are ubiquitous in the environment and can become allergens related to the onset of the disease. Some studies have shown that Staphylococcus aureus, Candida furfur and Candida albicans are common allergens. Second, the pathogenesis is generally believed that there are allergic reactions and non-allergic pathogenesis. The pathogenesis of allergic reactions is IgE-dependent type I and cellular immunity of type IV and S. aureus superantigenic effects; the pathogenesis of non-allergic reactions is vascular dysfunction, β-adrenergic receptor hypofunction, activation of phosphodiesterase isomers to reduce the level of intracellular cyclic squamate adenosine acid so that the immune response is not properly downregulated, resulting in a hypersensitive state to stimuli, allergens and microorganisms. Clinical manifestations AD is usually divided into 3 stages: infantile stage from 1 month to 2 weeks of age, called infantile AD; childhood stage from 3-10 years of age, called childhood AD; and youth and adult stage from 12-23 years of age, called adult AD.