PROSPECTS FOR PREVENTION
The high prevalence of asthma in the developed world and its rapid increases in the developing world call for a strategy for primary prevention. Strict antigen avoidance during infancy, once thought to be sensible, has now been shown to be ineffective. In fact, growing up from birth on a farm with domestic animals or in a household where cats or dogs are kept as pets appears to pro-tect against developing asthma. The best hope seems to lie inunderstanding the mechanisms by which microbial exposures dur-ing infancy foster development of a balanced immune response and then mimicking the effects of natural environmental expo-sures through administration of harmless microbial commensals (probiotics) or of nutrients that foster their growth (prebiotics) in the intestinal tract during the critical period of immune develop-ment in early infancy.