Babies spitting bubbles from their mouths is commonly caused by physiological factors such as underdevelopment of salivary glands and teething, but can also be caused by pneumonia and mouth ulcers. 1. Physiological factors: infant salivary gland underdevelopment, and the central nervous system is immature, the gag reflex and swallowing muscle development is not perfect, there will be the phenomenon of spitting bubbles, in addition to infants fast teething, it will cause the gum tissue swelling and discomfort, stimulate the salivary glands to appear reflex secretion increase, thus appearing mouth spitting bubbles phenomenon. 2. Pneumonia: infant respiratory immunity is poor, by the outside world germs infection, respiratory secretions increase, small infants are usually not manifested as a cough, but the mouth spitting bubbles, usually accompanied by fever, breathing faster. 3. Mouth ulcers: when the baby has mouth ulcers, the mouth is more painful, and the baby will appear to refuse milk, unwilling to swallow and other phenomena, thus appearing mouth spitting bubbles. The above are common causes of babies spitting up bubbles, if there are other accompanying symptoms, it is recommended to take the baby to the hospital to do the relevant examination, to clarify the cause of the disease.