Red spots all over the body after a fever in a 9-month-old baby may be caused by measles, toddler emergency rash, herpes simplex and other factors. 1. Measles: Measles is mainly a disease caused by measles virus infecting the mucous membrane of the upper respiratory tract. Infants usually first appear fever, cough, runny nose and other symptoms, may appear red maculopapular rash, the appearance of rash body temperature higher. 2. Childhood Acute Rash: Due to the poor resistance of infants, when they are infected by human herpesvirus type 6, it will trigger the symptom of red spots all over the body after fever. Pink, small, dense macules appear mainly on the abdomen and gradually spread to the limbs and face. After the rash appears, the fever gradually decreases and stops. There may be other causes for the red spots on the whole body of a 9-month-old baby with fever. It is recommended to go to the hospital in time for a complete examination to clarify the cause of the disease and then give targeted treatment or therapy.