1, non-disease factors: infant body temperature is easily affected by the external environment: high temperature (heat stroke), too much clothing, too little water, water loss (sweating, diarrhea), room air circulation, before and after strenuous exercise, and others, such as prophylactic injections may also cause fever. 2, disease factors: the most common viral and bacterial infections, such as respiratory tract, gastrointestinal tract, urinary tract infections. In addition to fever, it is also accompanied by symptoms of various systems. Such as respiratory tract infection, there can be runny nose, sore throat, cough; gastroenteritis manifested as abdominal pain, vomiting, diarrhea; in the urinary tract infection may appear frequent urination, urinary pain, lumbago phenomenon. The accompanying symptoms of the various systems of small infants is not typical, may only anorexia, spitting up, diarrhea and other phenomena, so the younger the child’s fever the more important to see a doctor. There are many other diseases that cause fever, such as prolonged fever can be seen in some rheumatic immune diseases, hematologic diseases, malignant tumors and so on. You should pay attention to observe your child’s fever pattern and accompanying symptoms, and go to the hospital in time for examination and early treatment.