affect their health. Taking complex human–environment interactions into account requires a new systems approach to environmental health decision making. With regard to human health and the factors that impact it, four overarching categories are basic needs, shelter factors, personal factors, and endogenous factors. All four are social determinants of health and play an interactive role in environmental health, yet only endogenous factors cannot be changed by individuals (Figure 1-2).
Basic factors are needs that are crucial to survival: having food to eat, water to drink, and clean air to breathe. At the most basic level of human functioning, these factors are the foundation for everything human beings do. The next level—shelter factors—includes items that, although not directly needed to live, can improve the quality of life, such as physical surroundings, like homes and schools; community; access to health care and hospitals; clean water for recreation; and the ability to be employed and earn a living. Personal factors, the third category, are less tangible in nature, such as exerting control over one’s life and making choices or decisions, the feeling of social cohesion, and establishing rela-