Human susceptibility to indoor contaminants

Indoor environmental pollutants can act as irritants, allergens, carcinogens, or infectious agents. This chapter focuses on human susceptibility to indoor environmental pollutants, here defined as inherent factors that alter exposure-response relationships. The host defense system is an important determinant of human susceptibility and is composed of two portions: nonspecific immunity and specific immunity. Pollutants elicit responses from many components of the human host defense system, and human susceptibility results from biologic variability in these components. Nonspecific immunity responds to stressors based on physicochemical properties. Components include mucociliary clearance, the epithelial barrier, airway surface fluid, and neural reflexes. Specific immunity recognizes and responds to unique peptide or carbohydrate sequences present on the foreign agent, and components of the response may include lymphocytes, basophils, mast cells, and immunoglobulins. Irritants typically stimulate nonspecific immunity, allergens stimulate specific immunity, and infecting organisms and carcinogens interact with both. Additional inherent factors that may alter the toxicity of an agent include genetic background, the presence of disease or specific organ pathology, age, gender, body weight, nutritional, hormonal, and central nervous system status. Understanding the basis for human susceptibility to indoor environmental pollutants can assist in implementing practical strategies for managing indoor air quality.