Red rashes on the body may be caused by eczema, urticaria, scarlet fever and other diseases. 1. Eczema: Inflammation of the superficial dermis and epidermis caused by a variety of internal and external factors, inflammation stimulation will lead to blood cell oozing out of blood vessels, erythema, pimples, etc., which may appear as red rashes on the body. 2. Urticaria: It is caused by various foods, drugs or other factors that lead to body allergy, so that the small blood vessels of the skin and mucous membranes dilate and increase the permeability, localized edema occurs, and there are bright red lumps of varying sizes on the skin, leading to the phenomenon of red rashes on the body. 3. Scarlet fever: mainly due to group A beta-hemolytic streptococcus infection causing the body to develop septic, toxic and allergic lesions, the skin will be evenly distributed diffuse pinpoint-sized red papules, resulting in a red rash. Red rash may also be seen in purpura, drug rash and other diseases. It is recommended that patients with a red rash go to a regular hospital in a timely manner to get a clear diagnosis and standardized treatment under the guidance of a doctor.