Red patches on the body may be caused by urticaria, salpingitis, cellulitis, eczema and other causes. 1. Urticaria: related to allergies, infections, mental and endocrine factors, manifested in the first self-conscious itching of the skin, itching areas will appear pale white or red masses, the skin surface is uneven, surrounded by redness. 2. Dengue: mainly related to bacterial infection, mostly manifested as unilateral erythema of the lower leg, with clear boundaries, and at the same time, there are symptoms such as heat, pain, redness and swelling, and the condition develops rapidly. 3. Cellulitis: a purulent infection caused by bacterial infection, manifested by localized redness, swelling, pain, elevated skin temperature, with no obvious demarcation of normal skin, some patients may be accompanied by chills, fever and other manifestations. 4. Eczema: related to genetic, environmental and other factors, mostly in the head, face, limbs and other parts of the body, can be manifested as redness, pimples, blisters, etc., fused into a piece, spreading to the surrounding area, accompanied by intense itching. There may be other reasons for the red patches on the body, it is recommended to go to the hospital in a timely manner to clarify the cause of the disease and follow the doctor’s instructions to standardize the treatment.