What can cause colic? Is it because of trapped gas?

What causes colic -- and why it only affects some babies -- remains a baffling subject. Some doctors view it as a natural developmental stage that babies can go through as they adjust to all the different sensations and experiences that come with life outside the womb. Others attribute it to an imbalance of bacteria in the gut. Another theory is that colic stems from an imbalance of the brain chemicals melatonin and serotonin. Colicky babies might have more serotonin, which makes intestinal muscles contract. You can read more about colic and how to handle it here: http://www.parents.com/baby/care/colic/colic-basics/