While there is no clear consensus on the cause of colic, most doctors agree that it has something to do with discomfort resulting from the baby's inability to regulate sleep. According to most experts who study colic, excessive crying may be a result of a baby's inability to easily transition between stages of the wake-sleep cycle.

The crying may occur as the baby is waking up or when the baby is trying to fall asleep. When the baby finds himself in this drowsy but not-quite-sleeping limbo, it's uncomfortable and frustrating. Many babies vent their steam by crying and screaming.

Currently, this is the most widely accepted theory of the cause of colic. Colic may very well have multiple causes, but scientists have not yet ascertained them.