A study published in the British Medical Journal (May 22, 2004; Vol. 328:1223) supports the idea that growing up in an overly sterile environment may increase the risk of developing allergies. The researchers found that children with greater exposure to environmental microbes—such as those living with pets or farm animals—were less likely to develop allergic skin conditions than children without such exposure.
Interestingly, this protective effect was not associated with common infectious illnesses. Children who experienced infections such as colds or diarrhea were actually more likely to develop allergic rashes. This suggests that immune benefits come from regular exposure to diverse, non-pathogenic microbes rather than from acute infections.
The study also found that having a larger number of siblings was associated with a lower risk of allergy. However, the findings suggest that this protective effect is not due to siblings transmitting infections, but rather to increased exposure to a broader range of everyday environmental microbes.
