Eczema is an inflammatory skin disease caused by a variety of internal and external factors with a pronounced tendency to exude, accompanied by a pronounced itchy rash that is prone to recurrence and seriously affects the quality of life of patients. This disease is a common dermatological disease, the prevalence of the general population in China is about 7.5%, the United States is 10.7%. I. Etiology and pathogenesis The etiology of eczema is still unclear. Endogenous causes include abnormal immune function (such as immune imbalance, immunodeficiency, etc.) and systemic diseases (such as endocrine diseases, nutritional disorders, chronic infections, tumors, etc.) and hereditary or acquired skin barrier dysfunction. Allergens, irritants, microorganisms in the environment or food, changes in ambient temperature or humidity, and sun exposure can trigger or aggravate eczema. Psychosocial factors such as stress and anxiety can also trigger or aggravate the pathogenesis of the disease is not clear. At present, it is mostly believed to be the result of a combination of internal and external factors based on internal factors such as abnormal immune function and skin barrier dysfunction. Both immune mechanisms such as allergic reactions and non-immune mechanisms such as skin irritation are involved in the pathogenesis. Microorganisms can trigger or aggravate eczema through direct invasion, superantigen action or induced immune response. The clinical manifestations of eczema can be divided into three phases: acute, subacute and chronic. The acute phase is characterized by erythema, edema on the basis of corn-grain papules, papules, water scars, vesicles and exudate, the center of the lesion is often heavy, and gradually spread to the periphery, and scattered papules, papules and scars, so the boundary is unclear. In the subacute stage, the redness and exudation are reduced, and the vesicular surface is infatuated and desquamated. Chronic eczema mainly manifests as rough hypertrophy, mossy changes, may be accompanied by pigment changes, hand and foot eczema can be accompanied by nail changes. The rash is generally symmetrically distributed, often recurrent, and the conscious symptoms are itchy rash, or even severe itching. Laboratory tests are mainly used for differential diagnosis and screening of possible causes, routine blood tests may include eosinophilia, increased serum eosinophilic cationic protein, increased serum IgE in some cases, allergen tests help to find possible allergens, patch test helps to diagnose contact dermatitis, fungal tests can identify superficial fungal disease, scabies tests can help to exclude scabies, serum immune Globulin test can help identify congenital diseases with eczema dermatitis lesions, bacterial culture of skin lesions can help diagnose secondary bacterial infections, etc., and skin histopathology should be performed when necessary. Fourth, the diagnosis and differential diagnosis of eczema is mainly based on clinical manifestations, combined with the necessary laboratory tests or histopathological examination. Special types of eczema are diagnosed according to clinical features, such as dry eczema, self-sensitivity dermatitis, coin-shaped eczema, etc.; non-specific ones can be diagnosed according to clinical sites, such as hand eczema, calf eczema, perianal eczema, breast eczema, scrotal eczema, ear eczema, eyelid eczema, etc.; generalized eczema refers to eczema that occurs simultaneously in multiple sites. The severity of eczema can be scored according to its size and the characteristics of the rash. It should be differentiated from the following diseases: (1) it should be differentiated from other types of dermatitis with specific etiology and clinical manifestations, such as atopic dermatitis, contact dermatitis, seborrheic dermatitis, bruising dermatitis, and neurodermatitis; (2) it should be differentiated from diseases with eczema-like manifestations, such as superficial fungal disease, scabies, polymorphic heliotrope, eosinophilic syndrome, pellagra, and cutaneous lymphoma; (3) it should be differentiated from rare congenital diseases with eczema-like (3) Differentiate from rare congenital diseases with eczema-like lesions, such as Wiskott-Aldrich syndrome, selective IgA deficiency, and hyper-IgE recurrent infection syndrome.