Evidence suggests that allergic
respiratory diseases such as
hay fever and
bronchial asthma have become more common world-wide in the last two decades, and the reasons for this increase are still largely unknown. A major responsible factor could be outdoor air pollution, derived from cars and other vehicles. Studies have demonstrated that urbanization and high levels of
vehicle emissions and westernized lifestyle is correlated with the increasing frequency of pollen-induced respiratory
allergy. People who live in urban areas tend to be more affected by pollen-induced respiratory
allergy than those from of rural areas.
Pollen allergy has been one of the most frequent models used to study the interrelationship between air pollution and respiratory allergic diseases. Pollen grains or plant-derived paucimicronic components carry
allergens that can produce allergic symptoms. They may also interact with air pollution (
particulate matter,
ozone) in producing these effects. There is evidence that
air pollutants may promote airway sensitization by modulating the allergenicity of airborne
allergens. Furthermore, airway mucosal damage and impaired mucociliary clearance induced by air pollution may facilitate the access of inhaled
allergens to the cells of the immune system. In addition, vegetation reacts with air pollution and environmental conditions and influence the plant allergenicity. Several factors influence this interaction, including type of
air pollutants, plant species, nutrient balance, climatic factors, degree of airway sensitization and hyperresponsiveness of exposed subjects.