If you have a red rash on your face after a fever, it depends on the number of rashes, whether there is itching, whether the temperature has gone down after the rash, whether there will be another fever, and whether there is a rash on your trunk and limbs, as well as whether there is herpes on your palms and mouth, in addition to the rash on your face. If the rash is simply on the face and there are not many of them and there is no itching, it may be caused by a simple viral infection. If the rash is large and itchy, it may be caused by allergies. If the rash is confined to the hands, feet, face, or mouth, you should also be alert for hand, foot, and mouth disease.