3 months old baby spitting may be normal physiological reflex or baby teething, respiratory tract infection, gastrointestinal discomfort, etc., as follows: 1, normal physiological reflex: because the baby’s mouth is shallow, and salivary glands are more developed, or baby breathing, swallowing movements are not well coordinated, resulting in baby drooling, spitting, etc.; 2, teething: stimulate oral salivary gland secretion increased; 3, respiratory tract infection: upper respiratory tract infection Causes throat discomfort, redness and swelling of the throat, resulting in babies not daring to swallow saliva, or lower respiratory tract infections producing large amounts of phlegm. The baby has good cilia function and can deliver phlegm to the mouth by swinging the cilia. However, since babies do not spit, sputum and saliva mix into foam, forming baby spitting symptoms; 4. Gastrointestinal discomfort: parasympathetic excitement and increased saliva secretion caused by gastrointestinal disorders.