Hygiene levels associated with wheezing, eczema in preschool infants
If you follow the concept of Th1/Th2 balance of the immune system (search prior Updates on the website for additional information on this topic) then a certain level of exposure to antigens (primarily bacterial) are required for healthy development of the Th1 system. This article supports this hypothesis. There is also ample additional evidence to suggest that a normal bacterial flora is also essential for this process, and that antibiotic use will disrupt this. I realize the above article comes to a different conclusion, but with research you always need to step back and look at the totality of the evidence–this is usually where the more real truth lies.
ADC — Abstracts: Sherriff et al. 87 (1): 26