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Chapter 5: Our vulnerable groups 5.1 Concepts As with all toxic substances, the adverse effects of air pollution vary between individuals. This imbalance reflects a complex set of intrinsic and external factors and is variously described as 'vulnerability', 'susceptibility' or 'sensitivity', terms which are used differently and often interchangeably. 1 Here, we use the term 'vulnerability' to express the broad range of determinants whereby the health impacts of pollution are unequal. These determinants include those innate to an individual, such as their age and their genetically regulated capacity to metabolise inhaled pollutants, and those that are acquired, such as the presence of respiratory or heart disease. Together, these influences are reflections of an individual's biological 'susceptibility'. In addition, vulnerability includes environmental, social and/or behavioural factors that determine an individual's level of exposure and their capacity to manage it; these factors include, for example, the proximity of one's home to an external source of pollution, co- exposures in the workplace, and access to preventive measures or healthcare. These concepts are depicted in Fig 14. The distinction between biological and environmental vulnerability, or innate and acquired susceptibility, is conceptually useful, but in truth it is somewhat artificial. For example, older individuals become more vulnerable because they have an age-related loss of antioxidant defence mechanisms in the 68 © Royal College of Physicians 2016 Fig 14. Concepts of vulnerability to the effects of air pollution. Modification or risk Biological susceptibility Vulnerability Environmental susceptibility Innate • Age • Sex • (Epi)genome • Etc Structural • Place of residence • Housing • Access to preventive strategies • Access to healthcare • Etc Behavioural • Occupation • Mode of travel • Commuting • Etc Acquired • Disease • Diet • Etc