A recent study from Cornell University challenges the widely accepted "hygiene hypothesis," which claims that exposure to a variety of microbes may protect individuals from diseases caused by allergens. The research, conducted in mice, indicates that adults' exposure to diverse microbes and allergens could actually worsen certain allergic conditions.
"Our data suggests that it's important to think about how we go through the world and protect ourselves from exposure to microbes, because depending on your condition, if you're moving from a clean to a dirty environment, or dirty to clean environment, you might have a different response in terms of developing allergic disease," said Avery August, professor of immunology at Cornell University and senior author of the study published in the Journal of Immunology.
The hygiene hypothesis proposes that growing up in less-clean environments—such as farms—may help prevent allergic diseases. Previous epidemiological and experimental studies have supported this idea. However, the new findings suggest that protection from microbial exposure is more complex than previously thought and may depend on factors such as age and timing.
For their research, scientists used "specific pathogen free" mice raised in sterile environments with minimal microbial exposure. These mice were then housed with store-bought mice accustomed to greater microbial diversity. Both adult and newborn pathogen-free mice were exposed to house dust mite allergens—a common model for studying asthma-like symptoms.
Results showed that adult mice exposed to microbes developed more severe allergic airway inflammation compared to newborns under similar conditions.
Researchers plan further studies to examine how age affects protection against allergies related to microbial exposure. They also aim to identify whether particular types of microbes influence disease development and if these findings are relevant for other illnesses.
