New BWH research shows that exposure to germs at an early age may help create a balanced immune system.

For many years, doctors and researchers have passed around a theory called the “hygiene hypothesis.” According to this notion, exposure of children to germs at an early age may help create a balanced immune system and prevent allergy and related diseases such as asthma and colitis later in life.

Yet there never was any direct research to back up the theory – until now. A new study by Brigham and Women’s Hospital (BWH) researchers provides evidence supporting the hygiene hypothesis and also helps explain how and why it might occur.

The researchers studied the immune system of mice lacking exposure to bacteria or any other microbes (“germ-free mice”) and compared them to mice living in a normal environment with microbes.

They found that the germ-free mice had exaggerated inflammation of the lungs and colon resembling asthma and colitis. But even more importantly, the researchers discovered that exposing the germ-free mice to microbes during their first weeks of life helped them build a normalized immune system for the prevention of diseases. This was not the case in mice that were exposed to microbes later in adult life. Furthermore, the disease protection that the mice with early-life exposure to microbes received proved to be long-lasting.

“These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life,” notes Dr. Richard Blumberg, chief for the BWH Division of Gastroenterology, Hepatology and Endoscopy, and co-senior study author, in collaboration with Dr. Dennis Kasper, director of BWH’s Channing Laboratory and co-senior study author. “Also now knowing a potential mechanism will allow scientists to potentially identify the microbial factors important in determining protection from allergic and autoimmune diseases later in life.”

Although the findings in mice are clear, the researchers caution that further research is still needed in humans. Nevertheless, the research provides a first step toward better understanding the recent global increase of allergic and autoimmune diseases in urban settings.

And it may also start to build a new perspective on germs – perhaps the right germs at the right time might be good for us after all.

– Linda W, MMQ

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