Fussing and crying are normal for infants, especially during the first three months. And the range for what is normal crying is difficult to pin down. In general, colic is defined as crying for three or more hours a day, three or more days a week, for three or more weeks.

Features of colic may include the following:

• Intense crying that may seem more like screaming or an expression of pain
• Crying for no apparent reason, unlike crying to express hunger or the need for a diaper change
• Extreme fussiness even after crying has diminished
• Predictable timing, with episodes often occurring in the evening
• Facial discoloring, such as reddening of the face or paler skin around the mouth
• Bodily tension, such as pulled up or stiffened legs, stiffened arms, clenched fists, arched back, or tense abdomen

Sometimes there is relief in symptoms after the infant passes gas or has a bowel movement. Gas is likely the result of swallowed air during prolonged crying.

The cause of colic is unknown. It may result from numerous contributing factors. While a number of causes have been explored, it's difficult for researchers to account for all the important features, such as why it usually begins late in the first month of life, how it varies among infants, why it happens at certain times of day and why it resolves on its own in time.

Possible contributing factors that have been explored include:

• Digestive system that isn't fully developed
• Imbalance of healthy bacteria in the digestive tract
• Food allergies or intolerances
• Overfeeding, underfeeding or infrequent burping
• Early form of childhood migraine
• Family stress or anxiety

Risk factors for colic are not well-understood. Research has not shown differences in risk when the following factors were considered:

• Sex of the child
• Preterm and full-term pregnancies
• Formula-fed and breast-fed babies

Infants born to mothers who smoked during pregnancy or after delivery have an increased risk of developing colic.

Colic does not cause short-term or long-term medical problems for a child.

Colic is stressful for parents. Research has shown an association between colic and the following problems with parent well-being:

• Increased risk of postpartum depression in mothers
• Early cessation of breast-feeding
• Feelings of guilt, exhaustion, helplessness or anger

Shaken baby syndrome

The stress of calming a crying baby has sometimes prompted parents to shake or otherwise harm their child. Shaking a baby can cause serious damage to the brain and death. The risk of these uncontrolled reactions is greater if parents don't have information about soothing a crying child, education about colic and the support needed for caring for an infant with colic.