Four-month-old baby with a low fever for three days can be seen in infectious diseases, non-infectious diseases, whether it can be “good” according to the condition of the judgment, such as acute upper respiratory tract infections caused by the possible self-healing. 1. Infectious diseases (1) acute upper respiratory tract infection: can be caused by viral infections, the above phenomenon can occur during the course of the disease, the disease is generally self-limiting, the fever can last for about 3-7 days to heal themselves, so this kind of cause of the above phenomenon may “get well on their own”, but some of the babies with bacterial infections need to be treated with anti-infectious treatment before the condition can be Improvement. (2) urinary tract infection: the child may show the above symptoms, general urinary tract irritation is not obvious, some babies may have crying symptoms during urination, the disease will not “get well on its own”, need to be actively and reasonably treated to avoid aggravation of the condition. 2. Non-infectious diseases: such as acute leukemia, the course of the disease can appear in the above manifestations, often repeated temperature fever variable, the disease generally will not “own good”, the progress of the disease may appear skin and mucous membrane hemorrhages, lymph node enlargement and other conditions, need to diagnose and carry out reasonable treatment. Low fever in babies can be seen in a variety of diseases, and it is recommended to actively consult a specialist physician for evaluation and judgment.