Can we live too clean a life? Is a little dust and fur a good thing?

A study by scientists at the University of Colorado-Boulder and in Germany offers support to the scientific idea called the “hygiene hypothesis,” which says living in an overly sterile environments might actually be bad for our health.

Their study in the Proceedings of the National Academy of Sciences found that children raised in rural areas with pets and bacteria-laden dust may have hardier immune systems and better mental health than city kids without pets. Researchers noted that it has previously been shown that country living during the development years can reduce the incidence of asthma and allergies.

In the study, 40 healthy German men ages 20 to 40 were split into two groups, those who lived on a farm with animals, and city dwellers who lived only with the species homo sapiens.

Then, all were exposed to the stress of giving a speech in front of a group that displayed no reaction. Afterward, they had to solve math equations while being timed.

At intervals before and after, their blood and saliva were sampled. While the country participants felt more stress, the city folk showed higher chemical signs of what researchers called an exaggerated, inflammatory immune response.

That immune response is known to put people at higher risk of mental health problems such as depression. Researchers said the results might not be surprising since our immune-regulatory response develops when we are young and is shaped by the microbial world.

So, parents, be forewarned. Your kids might now have a strong, science-based argument to support getting that cute dog or cat at the local animal shelter.