Why is allergy increasing?--environmental factors.

Data from epidemiological studies have shown that allergic conditions have increased over the last 30-40 years, particularly in developed countries, despite a decrease in the severity of grass pollen seasons. Other epidemiological studies suggest an interaction between allergic diseases and traffic pollution, and laboratory findings indicate that diesel exhaust particles enhance sensitivity to allergens. In an in vitro study, we found evidence to suggest that cigarette smoke may render the airway epithelium more susceptible to adverse effects of allergens. Evidence from other studies indicates that O3 and NO2, with or without SO2, can enhance the airway allergic response in susceptible individuals such as those with asthma and rhinitis. Studies investigating cellular and subcellular mechanisms suggest that pollutants are likely to influence the actions and interactions of a variety of cells, and lead to the synthesis of proinflammatory mediators that modulate the activity and functions of inflammatory cells.