Research studies have shown that the amount of "normal crying" during the first three months of life can range from about 40 minutes to 2 hours per day. This crying can be for a number of reasons, including things such as hunger, pain, overstimulation, or being tired (see Understanding a Crying Baby).
A baby with colic cries for longer periods and more often than a baby without colic. A couple of other differences between "normal" crying episodes and a baby with colic include:
- The cry has a distinct beginning and end
- The cry is louder, higher-pitched, and more intense
- The infant can't be soothed
- The infant's muscles are tense (such as clenched fingers, tight arms, and/or legs pulled up into the abdomen).
(Click Colic Symptoms for more information.)
Colic is reported to occur in between 8 percent and 40 percent of infants. Part of the reason for this wide range is that there is no standard definition of colic.
No one knows for sure what causes colic. Researchers have studied possible biological, social, psychological, and physical factors. However, no single factor has been shown to cause the condition.
Because babies with colic are otherwise healthy, it is not caused by a medical condition. It is also not caused by something that the parents are or are not doing.
Researchers have not been able to identify anything that increases the risk of a baby developing colic. Some of the factors that have been studied that have not shown any increased risk include:
- Bottle-fed versus breastfed infants
- Full-term versus pre-term babies
- The first versus the second child
- Siblings of an infant who had colic.
Two studies did show that infants exposed to tobacco smoke either in the womb or following birth were twice as likely to develop colic than those who were not.