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Remember what your mom used to say about not getting dirty when you play outside? Turns out she might be wrong. A new study out of Ohio State University (OSU), published in in the journal Frontiers in Immunology has found that getting up close — and a little dirty — with farm animals just might help us fend off illness.

The OSU researchers found that bacteria and other microbes found in the stomachs and intestines from rural Amish babies were far more varied than those from urban areas. The experiment, which is a first of its kind, discovered evidence of how a healthier gut microbiome could lead to a more robust evolution of the respiratory immune system.

“Good hygiene is important, but from the perspective of our immune systems, a sanitized environment robs our immune systems of the opportunity to be educated by microbes. Too clean is not necessarily a good thing,” said the study’s co-lead author Zhongtang Yu, a professor of microbiology in OSU’s Department of Animal Sciences and a member of the university’s Food Innovation Center.

In the study, Yu and his team collected fecal samples from 10 babies in Ohio, all approximately six months to a year old. Five of the babies came from rural homes which raised farm animals. The five urban babies were from the mid-sized city of Wooster. None of those had any known contact with livestock.

Based on the infants’ exposure to animals, and the fact that Amish tend to live a less decontaminated life than urban dwellers, the researchers expected a difference in gut microbes. However, what they had really wanted to know was how the differences might affect the development of the child’s immune system, which would prepare the babies to ward off diseases as well as allergy resistance and other immune-system complications.

Previous comparative studies of the Amish to urban populations have lead to a theory called the “hygiene hypothesis,” an idea that ultra-clean modern life — think antibacterial soap and hand sanitizer — has led to an increase in autoimmune and allergic diseases.

To study the babies gut microbes, the researchers used fecal transplants to colonize the guts of newborn pigs.

“The priming of the early immune system is much different in Amish babies, compared to city dwellers,” said Renukaradhya Gourapura, a co-lead author of the study.

“We wanted to see what happens in early immune system development when newborn pigs with ‘germ-free’ guts are given the gut microbes from human babies raised in different environments,” Gourapura said.

“From the day of their birth, these Amish babies were exposed to various microbial species inside and outside of their homes.”

What they found was a positive relationship between the diversified Amish microbes and a more-robust evolution of immune cells, particularly lymphoid and myeloid cells in the intestines.

A recent study published in Nature by scientists at the Weizmann Institute of Science has even shown that intestinal microbes, collectively termed the gut microbiome, may affect the course of amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease.