Spitting up and vomiting in babies have become a huge area of parental concern. After your baby swallows milk, it glides past the back of the throat into a muscular tube (the esophagus) and, from there, into the stomach. Infants are especially prone to reflux because:
Their stomachs are quite small so they are easily distended by the milk
The lower esophagus valve may be immature and may not tighten up when it should
There are a few things that might help:
1. Keep your baby upright after feeding for some time
2. Elevate whole baby's body when laying down (to let gravity help out)