THE FACTS

Colic is one of the most prevalent conditions of infancy: about 20 percent of all babies suffer the inconsolable bouts of crying that characterize it.

Yet no one really understands what makes a baby colicky. Scientists have investigated a number of causes — allergies, hormones in milk, even stress in the womb. But some now think it may stem from inflammation in the gut, perhaps a result of too many harmful bacteria and not enough beneficial ones.

A 2009 study, for example, found that colicky babies had gastrointestinal inflammation and traces of a bacterium in their guts that may have prompted it. Babies without colic had no inflammation and a greater diversity of beneficial bacteria.

So could higher levels of gut-friendly bacteria make a difference?

In a 2007 study, Italian researchers looked into this by examining 83 colicky babies who were breast-fed. Over 28 days, some of the infants were given simethicone, a medication that reduces gas; the others were given a supplement containing L. reuteri, one of the beneficial bacteria known as probiotics and often found in yogurt. At the end of the study, the babies who received the probiotic cried an average of 51 minutes a day, compared with about two and a half hours in the other group. A 2010 study had similar results.

“Gut microbiota changes induced by the probiotic could be involved in the observed clinical improvement,” the researchers wrote. Still, experts say they would like to see more studies.

THE BOTTOM LINE

There is evidence that probiotics may help relieve colic. ANAHAD O’CONNOR scitimes@nytimes.com