Eczema etiology is complex, allergenic factors are more, often not easy to identify, even if identified, it is not easy to avoid or eliminate, which leads to eczema stubbornly difficult to treat and easy to recur, in summary, mainly related to the following factors. 1, the disease has a genetic predisposition: allergic dermatitis, asthma, urticaria, etc.: can not tolerate life and work in many of the stimuli harmless to normal people, patch test can occur when a positive reaction to a variety of substances, even if the removal of certain allergens, eczema lesions are not easy to disappear quickly. 2, internal factors: internal infection foci: chronic cholecystitis, tonsillitis, gingivitis, rhinitis and sinusitis, intestinal parasitic diseases; endocrine and metabolic disorders, diabetes, menstruation, pregnancy, etc.; limb blood circulation disorders, varicose veins in the lower extremities, etc. 3, external factors: food: fish, shrimp, crab, beef and mutton, etc., inhalants: pollen, dust mites, fur, dander, etc.; microorganisms: purulent cocci on the body surface, superficial fungal infections; physical factors: sunlight, cold, humidity and heat and other climate changes; chemicals: cosmetics, detergents, etc. 4, different sites, different causes: hand eczema: in addition to atopic qualities, the onset of some patients may be related to factors such as occupation, emotions and climate. Detergents and other stimuli often make the condition worse. Breast eczema: often associated with breastfeeding and local irritation; stopping breastfeeding and local irritation can lead to rapid improvement of symptoms. Eczema of the vulva, scrotum and anus: due to the rich distribution of nerves and intense local itching, often due to excessive scratching and hot water scalding, resulting in long-term recurrent episodes. Sweating rash: the cause is unclear, in the past it was thought to be caused by excessive sweating of the hands and feet and retention of sweat in the skin, but now it is mostly thought to be an endogenous eczema-like reaction of the skin, which occurs in the spring and summer, with regular annual attacks and self-healing in winter. Systemic allergy to nickel and chromium metals and psychological factors are related to the onset of the disease. In conclusion, the development of eczema is often the result of the interaction of many endogenous and exogenous factors. Most scholars now believe that its pathogenesis may be related to late onset allergic reactions.