BACKGROUND There is growing public awareness regarding the risk associated with poor indoor air quality in the home and workplace. Because Americans spend approximately 22 hours every day indoors, susceptible individuals are at much greater risk of adverse health effects from chronic low levels of exposure to indoor air pollutants over time. Along with particulate matter, gases such as ozone, nitrogen dioxide, carbon monoxide, and sulfur dioxide; microbial and chemical volatile organic compounds; passive smoke; and outdoor ambient air are the most common types of air pollutants encountered indoors. OBJECTIVE To provide the allergists with necessary information that will assist them in making useful recommendations to patients seeking advice regarding indoor environmental triggers beyond traditional perennial allergens. METHODS Review of the literature pertaining to indoor exposure and health effects of gaseous and particular matter. RESULTS Indoor pollutants act as respiratory irritants, toxicants, and adjuvants or carriers of allergens. CONCLUSION The allergist should be prepared to evaluate patient exposure to allergic and nonallergic triggers and understand how outdoor air pollution is affecting indoor environments. This requires being familiar with methodologies for monitoring and interpreting indoor air quality and interpreting results in the context of the patients exposure history and advising patients about rational environmental control interventions.