Environmental factors and allergic airway diseases

A number of epidemiological studies show that in the last few decades, all over Europe, there has been a growing increase in allergic respiratory disease, which affects between 15 to 30% of the population. There is compelling evidence that this rise in allergic illnesses depends mainly on the type of the environmental pollution and on the typical lifestyle of western countries. Community-based studies comparing people living in former East and West Germany have proved a high prevalence of allergic respiratory disease in West German cities, with variances due to the differences in indoor and outdoor pollution. Ozone, nitrogen oxides, and respirable particulate matter (PM10) are the main components of photochemical smog, typical of western countries. They can lead to sensitization and the onset of allergic illnesses with direct and indirect mechanisms. The casual relationship between automobile traffic-generated pollution, in particular diesel exhaust particles which act as adjuvant on pollen sensitization, and the increase in allergic sensitization to pollens was proved by epidemiological observations, which were later confirmed by studies of animal laboratory exposure. Indoor environment is probably as important in increasing the prevalence of allergic disease. Different housing habits, energy-efficient buildings, and modern air-handling systems have reduced ventilation and produced substantial changes in indoor environment and an increased exposure to allergens (housedust mites, mould and pets dander in particular). Like outdoor pollution, tobacco smoke, formaldehyde, volatile organic compounds, fire burning products, and other chemicals can enhance allergic sensitization with direct and indirect mechanisms. Increased exposure to allergens in the early years of life can influence the immune regulation and the evolution towards a prevailing Th2 response. Recent epidemiological observations lead us to conclude that in the onset of allergic airway illnesses environmental factors can play a greater role than genetic predisposition. This revised version was published online in June 2006 with corrections to the Cover Date.