4 months old baby always spit bubbles for more reasons, mainly consider the following aspects: First, 4 months old child because the development of salivary glands are more mature, saliva secretion is abundant, while the child’s central nervous system is not mature enough to develop, swallowing function is poor, so will spit bubbles. The second aspect is that if inflammation occurs in the child’s respiratory tract, the inflammatory material will stimulate the salivary glands to secrete body fluids, thus appearing to spit bubbles. The third aspect, 4 months old baby’s intellectual development is more rapid, through the spitting tongue to explore the world, and spitting tongue more often can also lead to an increase in saliva bubbles.