Babies throw up, vomit or spit up for different reasons. For the most part spit up is caused by gas or the baby eating to much at one setting. Many infants have acid reflux as their stomachs are not ready to digest food.
Babies throw up because they have tiny stomachs and immature digestive systems. Unless your baby is in pain there is no need to worry. If they are in pain it may be reflux and you should see your doctor. It's nothing you can do anything about, so keep a burp rag handy!
a baby can vomit for many reasons one might be lactose in tolerent or a head bang is what doctors look at after a fall or just may be full constipated or needs soy products you may want to take them to doctor to change status of milk requirments or