Red rashes all over the body may be caused by allergic contact dermatitis, acute eczema, acute urticaria, common scarlet fever, early childhood acute rash and other factors. 1. Allergic contact dermatitis: If you come into contact with allergens such as pollen, willow flakes, animal fur, ultraviolet rays, etc., it leads to an over-immune response, causing a red rash all over the body, sometimes accompanied by itching and other symptoms. 2. Acute eczema: If the skin is exposed to sunlight, chemicals, dryness, high temperature and other external stimuli, it may cause skin inflammatory reaction, easy to appear the phenomenon of red rash all over the body. 3. Acute urticaria: due to genetic or autoimmune function abnormality, environmental changes and other causes of skin, mucous membrane small blood vessel dilation and increased permeability, thus appearing all over the body red rash phenomenon. 4. Ordinary scarlet fever: If the body is infected with group A beta streptococcus due to close contact with the sick person, causing ordinary scarlet fever, the phenomenon of red rash all over the body will also occur. 5. Childhood acute rash: If infants and young children are infected by viruses due to inhalation of pathogen-containing air and contact with patients and hidden infected persons, they will develop a red rash all over their bodies. If the symptoms do not subside for a long time, it is recommended to go to the hospital in time to identify the cause and follow the doctor’s instructions for standardized treatment.