The common causes of a baby’s red rash after a fever are toddler’s emergency rash, other infectious rashes and so on. 1. toddler rash: toddler rash is usually caused by viral infections, its typical symptom is that the sick baby first fever, fever lasts about 3 to 5 days, the baby suddenly fever, fever or the next day will appear all over the red rash. 2. other infectious rashes: if the baby because of cold, indigestion and other reasons lead to fever, after the fever body resistance decline, by bacteria, parasites, viruses and other pathogens, such as streptococcal infection caused by scarlet fever, infectious rashes can occur, manifested as a fever after a red rash. There may be other reasons for the baby to have a red rash after fever, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.