A four-month-old baby with a fever needs to have the cause clarified and treated accordingly. It may be related to upper respiratory tract infection, pneumonia and so on. If the fever is not high and the cause of the fever is unknown, it is usually not advisable to reduce the fever so as not to cover up the illness. It is recommended to go to the hospital in time to clarify the cause of the disease. 1. Upper respiratory tract infection: mostly caused by viral infections, if simple viral infections, more intensive care, more water, more rest, if necessary, take symptomatic treatment can be taken, such as low fever to take physical hypothermia, the temperature exceeds 38.5 degrees, you can use drugs such as acetaminophen to lower the temperature. If there is a bacterial infection, you can use penicillin, antibiotic treatment. 2. Pneumonia: mainly manifested as fever, chills, fatigue, cough, chest pain and other symptoms. Viral infections can also be relieved by using oral antiviral solution, etc. Bacterial infections can be treated with penicillin, cephalosporin and other drugs. In the case of mycoplasma infections, drugs such as azithromycin are required. The treatment of the cause of the fever also needs to be directed at the fever to reduce the heat treatment. The four-month-old baby fever may also have other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, give targeted treatment or treatment. The medication should be in accordance with the doctor’s prescription.