No one knows what causes colic, the intense pain and stomach cramping that commonly begins in otherwise healthy infants at about a month and disappears a few months later. But now researchers have found a possible explanation: the kinds of microbes that inhabit babies’ intestines.

Researchers at Radboud University and Wageningen University in the Netherlands collected nine stool samples from each of 12 colicky babies and 12 age-matched babies without colic over their first 100 days of life. All the babies and mothers were healthy. But as early as the first weeks, the scientists found significant differences in the intestinal microbes of colicky and noncolicky babies. Those with colic had more proteobacteria — including species that produce gas and inflammation — and fewer bifidobacteria, especially the lactobacilli known to combat inflammation.

The researchers, writing last week in Pediatrics, suggest that probiotic supplements, which contain beneficial bacteria and sometimes decrease symptoms, may work by displacing harmful bacteria.

But the lead author, Carolina de Weerth, cautioned against routinely giving probiotics to infants. “We actually haven’t determined causality,” she said. “We need randomized controlled studies to see if there’s a causal effect and to see if it’s safe.”