If your baby has a fever of 39.9 degrees Celsius, you should first give him or her oral antipyretics immediately, which can be ibuprofen or acetaminophen. If the baby’s hands and feet are cold, it means that the body temperature is still in the process of rising, so you should cover a little bit more and use warm water to warm up the hands and feet to promote circulation, if the hands and feet are warm and the body is sweating, it means that the body temperature is in the process of falling, so you can cover a little less to promote heat dissipation. In addition, if the baby is awake, you should try to let the baby drink more water, when the fever increases the apparent water loss of the skin, and after drinking more water, some of the heat will be excreted with the urine, in addition, you should go to the hospital and cooperate with the doctor to do the relevant examination.