Spitting up of saliva by a 3-month-old baby may be a normal physiological phenomenon or a manifestation of some diseases. Generally speaking, if the baby simply spits up saliva without other manifestations, it is related to the normal secretion of salivary glands in the baby’s mouth and the uncoordinated swallowing function of the baby. Because the saliva is too late to swallow inside the stomach, so the baby will spit saliva to the outside of the mouth through the form of spitting, which is a normal physiological phenomenon. Sometimes the baby spits, but the saliva is sticky, and at the same time the baby has coughing or crying, frequent choking, irregular breathing, sleep disturbance at night, these problems may be the performance of pneumonia, this time need to promptly go to the hospital.