Red patches on legs may be caused by chronic eczema, common type psoriasis, scarring, centrifugal annular erythema and other diseases. 1. Chronic eczema: the cause of this disease is not yet clear, it is a chronic inflammatory skin disease caused by internal and external multi-factors, and it is considered to be related to heredity, infection, allergy, immunity and so on. Chronic eczema patients can appear red spots, rough skin, hypertrophy, flaking, etc., can appear on the legs of the phenomenon of red patches. 2. Ordinary type psoriasis: the disease may be related to heredity, infection, immune abnormality and other factors. Patients with ordinary type psoriasis may have red plaques covered with silvery-white scales, which make the phenomenon of red plaques appear on the legs. 3. Scarring: When the legs are traumatized, such as burns, scalds, post-surgery fractures, etc., the skin may form hyperplastic scarring due to the shedding of scabs during the healing process, and red patches appear on the legs. 4. Centrifugal annular erythema: the cause of this disease is not yet clear, it may be caused by heredity, infection, internal diseases, etc. Patients may have round erythema-like lesions, the edges of which may be elevated, and red patches may appear on the legs. There are many reasons for red patches on the legs, and it is recommended that patients consult a doctor in time to identify the cause of the disease and then standardize the treatment.