Why Babies Spit Up Babies swallow air when crying and eating. This is why they burp. Sometimes, a baby will only swallow small amounts of air, not enough to make them burp. After a while, the little bubbles combine and are large enough to burp up. Any milk that is sitting on top of a big air bubble comes up too, causing the baby to spit up.
Some babies spit up frequently.
We have a muscle that keeps food from coming back up out of the stomach. In some infants, this muscle hasn't yet fully developed and these babies may spit up frequently. When these babies begin to walk, gravity will help keep food in the stomach. Since these babies generally have good appetites, the amount they spit up is annoying to parents. This may not be a problem to the infant.