Inconsolable crying—for more than three hours per day, more than three days a week, for longer than three weeks, specifically—defines colic. Between 10% and 40% of babies have colic, and luckily, most of them outgrow it by 3 to 6 months of age. Colic's cause is still unknown, but some likely triggers include intolerance to cow's milk protein or lactose and gastrointestinal immaturity or inflammation.