Environmental and occupational respiratory disorders
Health effects of air pollution

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The general public, especially patients with upper or lower respiratory symptoms, is aware from media reports that adverse respiratory effects can occur from air pollution. It is important for the allergist to have a current knowledge of the potential health effects of air pollution and how they might affect their patients to advise them accordingly. Specifically, the allergist–clinical immunologist should be keenly aware that both gaseous and particulate outdoor pollutants might aggravate or enhance the underlying pathophysiology of both the upper and lower airways. Epidemiologic and laboratory exposure research studies investigating the health effects of outdoor air pollution each have advantages and disadvantages. Epidemiologic studies can show statistical associations between levels of individual or combined air pollutants and outcomes, such as rates of asthma, emergency visits for asthma, or hospital admissions, but cannot prove a causative role. Human exposure studies, animal models, and tissue or cellular studies provide further information on mechanisms of response but also have inherent limitations. The aim of this rostrum is to review the relevant publications that provide the appropriate context for assessing the risks of air pollution relative to other more modifiable environmental factors in patients with allergic airways disease.

Section snippets

Classification of air pollutants

Air pollution derives from a variety of sources, of which the combustion of fossil-fuel products is the principal source. Air pollutants can be classified by their source, chemical composition, size, and mode of release into indoor or outdoor environments. The examples listed in Table I distinguish between primary versus secondary, indoor versus outdoor, and gaseous versus particulate pollutants. Pollutants directly emitted into the atmosphere are known as primary pollutants, whereas pollutants

Mechanisms of adverse health effects

The exact mechanism or mechanisms by which air pollutants cause adverse health effects are complex and not properly understood. A number of possibilities are listed in Table III. One mechanism of action is how reactive oxygen species cause inflammation. Fig 1 shows the hierarchic oxidative stress model, in which incremental doses of PM sequentially induce protective and injurious cellular responses.16 Oxidative stress is defined as a depletion of intracellular glutathione, leading to

Diesel exhaust particulate matter

Recent epidemiologic, human, and animal model studies have demonstrated that diesel exhaust particulates (DEPs) increase airway inflammation and can exacerbate and initiate asthma and allergy. Diesel combustion results in production of DEPs, nitrogen oxides, and precursors of ozone, all of which are harmful to the lung.

Because of the complex nature of diesel exhaust composition, a primary obstacle has been obtaining an accurate measure of exposure. Most studies have used traffic exposure as a

Interaction between allergen and pollutants

Four major issues concerning the interaction of outdoor pollutants and allergens include the following: (1) epidemiologic studies of pollution and aeroallergens on the genesis of asthma; (2) epidemiologic studies of pollution and aeroallergens on the exacerbation of asthma; (3) experimental studies on the adjuvant effect of pollutant particulates (DEPs) on specific TH2 responses; and (4) the role of pollution and global warming on natural allergen production.

Since 1997, there have been a number

Conclusions

Although early epidemiologic studies of the effects of air pollution on human health provided only associative data, the body of current scientific data now clearly delineates the role of pollutant-mediated adverse interactions in human allergic airways diseases.

The allergist–clinical immunologist should be keenly aware that both gaseous and particulate outdoor pollutants might aggravate or enhance the underlying pathophysiology of both the upper and lower airways. Although the health effects

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