Via NBC News…

“But a surprising new study suggests that exposure to cat dander, a wide variety of household bacteria — and even rodent and roach allergens — may help protect infants against future allergies and wheezing.

Interestingly, contact with bacteria and dander after age 1 was not protective — it actually increased the risk.

“It was the opposite of what we expected,” said Dr. Robert Wood, chief of the division of allergy and immunology at the Johns Hopkins Children’s Center and co-author of the study in the Journal of Allergy and Clinical Immunology. “We’re not promoting bringing rodents and cockroaches into the home, but this data does suggest that being too clean may not be good.””