The study, co-authored by researchers from the University of Ulm in Germany and the University of Colorado Boulder, adds to mounting evidence supporting the "hygiene hypothesis," which posits that overly sterile environments can breed health problems.
The research also suggests that raising kids around pets might be good for mental health -- for reasons people might not expect.
"It has already been very well documented that exposure to pets and rural environments during development is beneficial in terms of reducing risk of asthma and allergies later in life," said co-author Christopher Lowry, a professor of integrative physiology at CU Boulder. "This study moves the conversation forward by showing for the first time in humans that these same exposures are likely to be important for mental health."
For the study, led by University of Ulm Professor Stefan Reber, the scientists recruited 40 healthy German men between 20 and 40 years old. Half had grown up on a farm with farm animals. Half had grown up in a large city without pets.
