The baby suddenly has fever without other symptoms, there may be several reasons: 1. At the beginning of the cold, the child can first have fever as the main symptom and no other manifestations such as coughing, coughing and runny nose. But as the fever subsides in about 2-3 days or after the acute phase, the child will have symptoms of upper respiratory tract infection such as cough, runny nose, sneezing, runny nose, etc.; 2. In gastrointestinal colds, the child may have early symptoms of fever, accompanied by loss of appetite, followed by the possible occurrence of nausea, vomiting or diarrhea and other symptoms. In this case, after giving antipyretic drugs and controlling the diet, the child can generally improve. The child may have a sudden onset of high fever, followed by vomiting and other symptoms; urinary system infection, after the fever can appear urinary frequency and pain. According to the actual clinical examination, the diagnosis and treatment will be made after the corresponding examination.