37.8°C in a 7-month-old baby is usually abnormal and is classified as a low-grade fever. The symptoms of low fever may be caused by physiological factors, infectious factors, pulmonary infections and other factors. 1. Physiological reasons: such as the summer heat, the baby dressed too thick and other reasons can lead to the baby to reduce heat dissipation, which will cause fever, physiological causes without medication, only need to pay attention to the baby to prevent heat stroke, moderate reduction of clothing can be. 2. Infection: when the human body is infected by bacteria, viruses, fungi, mycoplasma, chlamydia and other pathogenic microorganisms, which can lead to excessive body heat production, thus causing fever. 3. Non-infectious causes: when the baby suffers from leukemia, systemic lupus erythematosus can appear fever, and will be accompanied by the corresponding clinical symptoms and manifestations of the disease. Baby low fever is not normal, if the symptoms are not relieved for a long time, you need to consult a doctor for a clear diagnosis, follow the doctor’s instructions for targeted treatment, so as not to miss the opportunity for treatment.