Unless you’ve been living under a rock for the last few years, you’ve probably heard about the health benefits of yogurt and other fermented foods. Clinical trials have found that probiotics (helpful bacteria) can help ease a range of symptoms. But what they haven’t found is how, exactly, they work. Now scientists writing in the journal Applied and Environmental Microbiology have got a theory.

The bacterial strain called Lactobacillus paracasei DG grows naturally in our mouths and guts. It’s also a common ingredient in probiotic supplements and so-called functional foods like probiotic yogurt. We’re happy to buy it and consume it, but we don’t know what makes it tick.

Researchers at Italy’s Università degli Studi di Milano and the University of Huddersfield in the UK theorized that L. paracasei DG was secreting some strange chemical compound called an exopolysaccharide (EPS). They searched through the bacterium’s DNA and, sure enough, found genes that make EPS.

The next step was to figure out what kind of EPS it was and what it did. They conducted chemical tests and nuclear magnetic resonance to examine the EPS at a molecular level. They found that a large portion of the compound was made of rhamnose, a sugar commonly found in probiotic strains.

Next, the team administered the EPS to living human immune cells and watched to see how they would react. Because probiotics are often used to ease symptoms of inflammation, it might be expected that the EPS would be a calming influence, but the opposite was true: The presence of the compound triggered a release of inflammatory chemicals from the immune cells.

Coauthor Andrew P. Laws says this seemingly counterintuitive finding actually makes a lot of sense. "We have evidence that our polysaccharides bind to and mildly activate the receptors which release pro-inflammatory messengers," he said in a statement. "We believe that this generates a lesser inflammatory response than what would occur if the same receptors were activated by pathogenic bacteria."

It’s a strange strategy, but it’s not completely unheard of. Scientists studying the “mind-control” germ Toxoplasma gondii recently reported that the parasite uses a very similar technique to elude detection within the body of its host.