Colic 101: What It Is and What to Do

What Causes Colic?

What causes colic -- and why some babies experience it and others don't -- remains a mystery. Some doctors view it as a natural developmental stage that babies can go through as they adjust to all the different sensations and experiences that come with life outside the womb. (Dr. Karp calls this "the fourth trimester.") Others attribute it to an imbalance of bacteria in the gut.

Yet another theory is that colic stems from an imbalance of the brain chemicals melatonin and serotonin. Colicky babies might have more serotonin, which makes intestinal muscles contract, says Marc Weissbluth, MD, professor of clinical pediatrics at Northwestern University School of Medicine and author of Your Fussy Baby (Ballantine). (One reason colicky babies can fuss more at night, he explains, is that serotonin levels peak in the evening.) This imbalance, the theory goes, naturally resolves when babies start making melatonin, which relaxes intestinal muscles. Babies get ample melatonin from Mom in utero, but levels drop after birth until baby starts producing it on her own at 3 to 4 months -- interestingly, around the same time that colic typically disappears. "This hypothesis should reassure mothers that they didn't cause colic," Dr. Weissbluth says. "It takes away the guilt that you're doing something wrong and aren't able to soothe your baby."