Every breath carries a mix of chemicals shaped by the body’s metabolism. A new study suggests that some of those molecules may come from an unexpected source: the microbes living in the gut. By analyzing exhaled breath from children and mice, researchers found that chemical signals produced by gut bacteria show up in breath samples. Those signals reflected the composition of the gut microbiome and, in some cases, pointed to bacteria associated with asthma, which affects an estimated 5 million U.S. children.

The findings, published in Cell Metabolism, land amid growing evidence that disruptions in the gut microbiome are linked to a range of diseases, from metabolic disorders to immune conditions. Yet tracking those microbial changes typically requires stool samples and genetic sequencing, making routine or rapid monitoring difficult outside research settings. Breath-based detection, the authors suggest, could offer a faster, less invasive window into microbial activity.