The causes of persistent low fever in babies are usually considered to be bacterial, viral and other infectious factors and non-infectious factors such as immune dysfunction and hyperthyroidism. 1. Infectious factors: bacterial infections, viral infections, parasitic infections, etc. may cause the child’s low fever persists, the most common is tuberculosis infection. In addition, intestinal infections, urinary tract infections and other infections in different parts of the body can not be ruled out. 2. Non-infectious factors: the child may have endocrine diseases such as hyperthyroidism or immune system diseases, which may cause neuroendocrine dysfunction resulting in persistent low fever. In short, when the symptoms of prolonged hypothermia do not go away, you should consult a doctor for a clear diagnosis and treatment under the doctor’s professional guidance.