Being on a restrictive diet is not the hardest part about having celiac disease, an autoimmune disorder that inhibits my ability to properly digest gluten. Far worse is the doubt and blame I regularly encounter upon mention of my condition to others. There are those whose eyes narrow with skepticism as they tell me how crazy it is that everyone is suddenly gluten free and how a little crumb of wheat can’t really hurt. And there are those who arrogantly shrug, and then go on to explain that if parents would stop being so neurotic about cleanliness there wouldn’t be so many people with allergies and autoimmune diseases today.

The latter group have likely heard about the hygiene hypothesis, which posits that a lack of exposure to bacteria and viruses in early childhood impedes our immune systems’ ability to develop properly, causing excessive immune responses to things that aren’t actually threatening (like gluten). Scientists began looking into this idea in the late 1980s, and since then evidence has steadily mounted that some of us live in a world too clean for our own good. Over the years, many of the headlines about this hypothesis have focused on personal hygiene, sending the message that all those peanut-free classrooms might not exist if parents could learn to put down the Purell. Now a new study shows that while our individual habits are a factor in autoimmune disorders, they’re hardly the only cause.

Researchers from the Broad Institute of MIT and Harvard collaborated with teams from the University of Helsinki and Aalto University in Finland, the Novartis Institute of Biomedical Research, and other organizations around the world, to examine the gut microbiomes of infants in three geographically similar, but socioeconomically different places. These include Finland, which is wealthy and modern, Estonia, a country that has experienced rapid economic growth in the past two decades, and Russian Karelia, which is relatively agrarian and poorer than the other two. They recruited a group of over 222 infants in total, and collected monthly stool samples from them over the course of three years. These samples were examined to identify and quantify the type of bacteria in the individual infants’ guts—effectively telling the researchers which types of bacteria each infant had been exposed to. They also asked the families about breastfeeding, diet, allergies, infections, and family history. The goal was to see whether or not there was a significant difference between the microbiomes in Finland, where there is a high incidence of autoimmune disorders, and Russian Karelia, where there is a low one. There was. And as suspected, four times as many Finnish children tested positive for antibodies that make them more likely to develop type 1 diabetes than Russian children. (Estonian children had a high rate as well.)

So why the difference? It wasn’t diet or breastfeeding, both of which were controlled for in the study. (In fact, the Finnish mothers nursed longer than the Russians.) Instead, the scientists believe there is likely “a complex interplay of environmental factors” behind the children’s different microbiomes, which can only partially be explained by lifestyle choices. As Mikael Knip, a professor of pediatrics at the University of Helsinki and the study’s senior author, told the New York Times, children in Russian Karelia, many who grow up drinking untreated well water, are exposed to a wider variety of pathogens and potentially helpful microbes than Finnish children. This isn’t because Russians are all free-range parents who are chill about germs and Finns are all germ-phobic helicopter parents, but because there are simply more microbes to be exposed to in Russian Karelia. This is affected not only by present conditions, but also by the choices of previous generations: The vaccinations taken and food eaten by our grandparents contributed to the makeup of our microbiome today.

According to Tommi Vatanen, a graduate student at the Broad and the University of Aalto and co-first author of the study, this doesn’t mean parents are off the hook. He told me that parents should avoid putting their children on antibiotics whenever possible, and be OK with things like dogs licking their faces and the occasional ingestion of dirt. “What we know is that parents shouldn’t be blaming themselves, but they shouldn’t be too careful either,” Vatanen said.

And because the cause isn’t simple, the solution isn’t either. Experts don’t recommend that parents should put the brakes on basic hygiene practices like hand-washing for the sake of their children’s immune systems. The conditions that are best for avoiding autoimmune disorders aren’t necessarily the best for overall health. The researchers who wrote this study and others working in the field hope to figure out the precise relationship between our gut microbiomes and our immune system, so that they can develop better preventive treatments in the future. Sanitary conditions and a lower prevalence of autoimmune diseases “don’t have to be mutually exclusive,” Vatanen said. Future studies will help them figure out how to get the best of both worlds.