Eczema is a non-infectious inflammatory skin disease caused by a variety of internal and external factors. Its most typical clinical features include intense itching, a polymorphic rash, often symmetrical distribution, and a pronounced tendency to exude during acute attacks, while chronic onset or prolonged course of the disease is characterized by hyperplasia and hypertrophy. First of all, the occurrence of eczema is mostly mediated by allergic reactions, when the skin allergic reaction will produce a large number of local histamine and inflammatory mediators, such substances can lead to severe itching at the site of the lesion. At the same time, the occurrence of allergic reactions is not only induced by external factors, but also has an obvious basis of endogenous susceptibility, which, in layman’s terms, means that patients with eczema tend to be allergic; and eczema itself is an “inside-out” disease, so both sides of the body are susceptible to symmetrical rashes due to their intrinsic basis of reciprocity. In addition, because eczema is chronic and prone to recurrence, the degree of inflammatory response is characterized by dynamic evolution, so eczema can be divided into three categories: acute eczema, subacute eczema, and chronic eczema from the course and clinical characteristics. When eczema develops, it can develop in any one type and evolve to other types. Therefore, the lesions of eczema are clinically diverse and significantly polymorphic. In the acute phase, the rash develops rapidly, the inflammatory response of the lesions is heavy, tissue edema is evident, and plasmacytic exudate is easily seen. In contrast, in the chronic phase or chronic onset, eczema lesions develop slowly and show a marked tendency toward hyperplasia, hypertrophy, and infiltration. Therefore, eczema can be accurately identified by grasping the typical clinical features of eczema and understanding its causes.