There is no agreed-upon definition for infantile colic. Most healthcare providers consider an infant to have colic when he or she cries for more than three hours straight at least three days per week for more than three weeks but has a clean bill of health otherwise. This is known as the "rule of three," or the Wessel criteria.
No one knows for sure what causes infantile colic. Researchers have studied possible biological, social, psychological, and physical factors, but no single factor has been shown to be responsible. Because babies with colic are otherwise healthy, it is not caused by a medical condition. Colic is also not caused by something that the parents are or are not doing.
You can take comfort in knowing that colic will not last forever. Typically speaking, the condition peaks around six to eight weeks and then goes away around the baby's third month (symptoms get better in 60 percent of infants by month three and 90 percent of infants by four months of age). It often stops as mysteriously as it began.
(Click Infant Colic for a more in-depth look at this condition and how it is diagnosed. This article also offers tips for how to cope with a baby who has colic and possible risk factors.)