A new study of mice is adding weight to notion that exposing kids to germs in early childhood helps toughen up their immune systems and lowers their risk of developing allergies, asthma, colitis and other immune-related disorders later in life.
The new research on the so-called “hygiene hypothesis” was conducted at Brigham and Women's Hospital in Boston and published in the journal Science.
The Boston researchers studied mice bred in a sterile “germ-free” environment and those raised in a normal laboratory setting. They bred both groups of mice to develop forms of asthma and inflammatory bowel disease and compared their immune systems.

The researchers found the mice exposed to germs in their first few weeks of life developed less severe symptoms of asthma and bowel disease than those raised in sterile, germ-free environments.
"These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life," said Dr. Richard Blumberg, one of the study team’s leaders. “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."
The researchers suggested the “hygiene hypothesis” may explain why there has been a dramatic increase in asthma, allergies and other autoimmune diseases in urban areas.
The study was funded, in part, by the National Institutes of Health.