The concept of exposing infants to germs in order to build up immunity is known as the hygiene hypothesis. Now, researchers of Brigham and Women’s Hospital (BWH) have come up with evidence supporting the hygiene hypothesis for the first time.

They studied the immune system of ‘germ-free mice’ and compared them to mice living in a normal environment with microbes, the journal Science reported.

They found that ‘germ-free mice’ had exaggerated inflammation of the lungs and colon resembling asthma and colitis, respectively, caused by the hyperactivity of a unique class of T cells (immune cells).

These immune cells had been previously linked to these disorders in both mice and humans, said a university statement.

Most importantly, researchers discovered that exposing the germ-free mice to microbes during their first weeks of life, but not when exposed later in adult life, led to a normalized immune system and prevention of diseases.

Moreover, the protection provided by early-life exposure to microbes was long-lasting, as predicted by the hygiene hypothesis.

“These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life,” said Richard Blumberg, chief for the BWH Division of Gastroenterology, Hepatology and Endoscopy, and study co-author, working with Dennis Kasper, director of BWH’s Channing Lab.

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