To prevent allergies, should towns be moved to the countryside?

Several recent cross-sectional epidemiological surveys have demonstrated a significantly lower prevalence of asthma, allergic rhinitis and atopy in fa rmers compared to people living in rural areas without farming activities. This protective effect does seem to be related to contact with livestock an d cattle through regular exposure to Gram negative bacteria and endotoxins, which stimulate the Th1 pathways. However such compounds have detrimental effects in patients with established asthma. (C) 2001 Editions scientifique s et medicales Elsevier SAS.