The prevalence and incidence of allergic diseases have increased in Europe during the last decades, as in most industrialized countries in other parts of the world. Persistent exposure to traffic related air pollution and especially particulate matter from motor vehicles has often been discussed as one of the factors responsible for this increase. This view seems to be supported by recent human and animal laboratory-based studies, which have shown that particulate pollutants, and in particular diesel exhaust particles, can enhance allergic inflammation and induce the development of allergic immune responses. However, the results from epidemiologic research provide a more complex picture.
It has been clearly shown in many studies that traffic related air pollution contributes to increased mortality risk; in particular in relation to cardiopulmonary causes. Traffic related air pollution also increases the risk of non-allergic respiratory symptoms and disease. However, for allergic symptoms and illnesses like asthma, allergic rhinitis, atopic dermatitis, wheeze, and allergic sensitization less consistent results have been found. This is the reason why the World Health Organisation concludes cautiously that traffic related air pollution may increase the risk of allergy development and may exacerbate symptoms in particular in susceptible subgroups. This review concentrates on recent epidemiologic studies on the long-term effects of exposure to traffic related air pollution on allergic disease in Europe.
In conclusion, the evidence for an increased risk for asthma and hay fever still is weak but seems to be strengthened a little. However, many questions are left open.
GSF-National Research Centre for Environment and Health, Institute of Epidemiology, Neuherberg, Germany
Correspondence to Dr Joachim Heinrich, GSF-Institute of Epidemiology, POB 1129, D-85758 Neuherberg, Germany Tel: +49 89 3187 4150; fax: +49 89 3187 3380; e-mail: Joachim.Heinrich@gsf.de