The cause of colic is not known. No single factor has been identified, although many different factors appear to be associated with colic.

Colic affects infants of both genders, full-term and premature babies, as well as those who are breastfed and bottle-fed. Colic affects the infants of first-time parents as well as those of more experienced parents. There is little evidence that colic is associated with allergies or food intolerance (e.g., lactose intolerance), although infants with allergies can also have colic.

It was initially assumed that colic was caused by gas. Research now indicates that gas buildup may occur in babies with colic because they swallow a great deal of air during prolonged crying spells. In addition, certain feeding techniques (e.g., infrequent burping, swallowing of air during feedings) may aggravate gas buildup in infants with colic.

Colic appears to be associated with oversensitivity to stimulation. This includes environmental stimuli (e.g., bright lights, loud noises, lots of activity) and new experiences (e.g., meeting new people). One theory is that colic occurs when the stimulation babies are exposed to throughout the day is released – in the form of crying – in the evening.

An infant’s sensitivity to stimulation may be affected by their temperament (unique emotional disposition), which affects the way a child handles stress. Overly sensitive children may react strongly to changes in routines or stimuli that startle or frighten them. In addition, the developing nervous system of a child may make a baby more sensitive to stimuli such as bright lights and loud noises.

Immature digestive systems in babies may also be related to colic. Digestive systems that are not yet fully developed can affect the time it takes food to pass through the digestive tract and cause strong intestinal contractions and stomach pain.

Other factors believed to play a role in the development of colic for some infants include:

• Hormones (e.g., serotonin levels)
• Levels of emotional tension in the household
• Changes in feeding/comfort routine
• Anxiety, anger, frustration or excitement of the baby
• Nursing mother’s diet

Exposure to tobacco smoke has been linked to an increased risk of colic, according to some studies. Smoke is associated with a rise in the level of the hormone motilin in the blood, which can increase contractions of the stomach and intestines. Babies may be exposed to smoke while still in the womb, via a mother’s breast milk, or by being around a smoker after birth.

Other studies also have indicated that maternal stress during pregnancy, especially in the last trimester (last three months), may contribute to colic in some babies. More research is needed to confirm this link.