It's appropriate that we should still call this condition by its medieval name "colic," since we know about as much about its causes today as we knew 800 years ago.
A colicky baby is one who cries a lot and can't be pacified. Technically, if a baby cries for more than 3 hours a day, more than 3 days a week for at least 3 weeks, it's colic. Colic affects boys and girls equally and tends to run from the age of 3 weeks to the age of 3 to 4 months.
There has been much research to find what it is that makes colicky babies cry, but the answer remains elusive. Abdominal pain is involved in most cases, and sometimes the baby just has gas.
Colic is not due to a disease. Colicky babies are typically healthy and full of energy. Even after extensive testing, no medical causes have been found. One theory is that an underdeveloped digestive tract is responsible. Others blame abdominal gas, food allergies, or noise and distractions interfering with sleep. By looking at the various remedies that have been found to help, we can guess it's a mixture of these factors. Research also suggests that some crying is just a matter of temperament or nervous system maturation: some babies just cry more than others.
Other factors that have been found in some cases to have an influence on babies include:
The crying of a colicky baby is often high-pitched, grating, and piercing, even compared to normal infant crying. Neither food nor attention can stop it. Your baby's face may be red, the fists may be clenched, and the knees may be tucked up into the abdomen.
The crying goes on for at least an hour, and sometimes as long as 4 hours. It often starts at the same time each day, usually late afternoon or early evening (unfortunately, when the parents are most tired). Sometimes, the baby passes gas or a stool shortly before or after calming down.
Colic is generally at its worst around the age of 4 to 6 weeks. If your baby is still colicky after 3 months, or cries nonstop for more than 3 or 4 hours, some other condition may be causing real discomfort and you should take the baby to the doctor. You may want to take your baby to the doctor when colic first appears, just for a checkup to ensure you are not overlooking something that can be effectively treated, especially if this is your first baby.
Always see the doctor if your baby cries for more than 4 hours, has a fever, becomes lethargic, vomits more than normal, or has bloody stools. These are not signs of colic.