Allergic dermatitis is due to the body’s allergic reaction to allergens, generally allergic dermatitis is not a separate disease, eczema, atopic dermatitis, contact dermatitis and other diseases are related to allergic reactions; and seborrheic dermatitis may have a certain degree of allergic factors involved, but does not belong to the allergic diseases, and the above allergic dermatitis there are more differences. 1. Eczema: due to a combination of various internal and external factors, it occurs in summer and winter, and can be characterized by erythema, papules, infiltrative thickening of the skin, itching, etc. Skin patch test helps to find allergens, and dermatopathological biopsy helps to diagnose it. 2. Atopic dermatitis: atopic dermatitis with family heredity, with chronic recurrence, different symptoms and onset of different parts of the body at different ages, but the basic feature is eczema-like dermatitis, accompanied by intense itching. 3. Contact dermatitis: caused by skin contact with animal, plant, chemical and other exogenous substances, the scope of dermatitis is usually consistent with the contact material, the boundary is clearer, can be manifested as erythema, papules, edema, blisters, vesicles, oozing and other symptoms, often accompanied by itching, burning, swelling and pain. 4. Seborrheic dermatitis: the etiology is unknown, it may be related to Malassezia, sebum level and immune response, etc. It is commonly seen on the scalp, face, behind the ears and other parts of the sebaceous glands with strong secretion, and is not family hereditary, and it manifests itself in the form of dryness, dampness, or oily scales, and the itching is not strong. Allergic dermatitis has a wide range, and seborrheic dermatitis has a lot of differences, it is recommended that patients with related symptoms seek medical attention in a timely manner, under the guidance of the doctor for relevant examinations, in order to clarify the diagnosis and symptomatic treatment.