Four-month-old babies with low-grade fever should have their body temperature measured regularly to understand the specific changes in temperature. Infants with a body temperature over 37.5℃ should consider infection and fever symptoms, which are often accompanied by poor mental health, drowsiness, vomiting, coughing and other uncomfortable symptoms. If the body temperature is between 37.5 and 38.5℃, physical cooling treatment should be given to reduce the amount of clothes worn to facilitate heat dissipation, and warm water baths and fever patches should be given to help reduce the temperature. If your baby’s temperature continues to rise above 38.5℃ and his mental state is poor, you need to go to the hospital and have a pediatrician perform relevant physical and laboratory examinations to clarify the cause of the fever and infection before administering targeted medication.