Health inequalities arise from multiple interacting causes rather than one universal mechanism. Important determinants include income, education, employment, housing, working conditions, neighbourhood environment, social support, access to healthcare, exposure to discrimination, health behaviours, environmental pollution and underlying biological susceptibility. These factors influence one another and can accumulate across the life course. A person's health is therefore shaped not only by medical care or individual choices but also by the conditions in which they are born, grow, live, work and age. Different diseases have different causal pathways, so the relative contribution of each determinant varies. The same social factor can influence several health outcomes through different biological, behavioural and environmental mechanisms.
Socioeconomic position is a major determinant of health inequality. Income affects the ability to obtain adequate housing, nutritious food, heating, transport, recreation and other resources that support health. Education can influence employment opportunities, health literacy and the ability to navigate complex systems, while employment affects income, occupational exposures, job security, control over working conditions and access to social protection. Material disadvantage can therefore influence health directly through living conditions and indirectly through chronic stress, restricted opportunities and reduced access to protective resources. Socioeconomic circumstances can also change over time, and prolonged or repeated disadvantage may produce cumulative effects rather than a single short-term exposure.
Housing and the physical environment can contribute substantially to unequal health outcomes. Poor-quality housing can involve damp, mould, inadequate heating, overcrowding, poor ventilation or safety hazards. These conditions can contribute to respiratory disease, injuries and other health problems. Neighbourhoods may differ in air pollution, traffic exposure, green space, noise, access to healthy food, recreational facilities and public transport. Environmental risks can therefore be geographically concentrated. People with fewer economic resources may also have less ability to move away from unhealthy environments, creating an interaction between socioeconomic inequality and environmental exposure.
Working conditions can produce health inequalities through physical, chemical, biological and psychosocial hazards. Occupational exposure to dust, asbestos, solvents, radiation, infectious organisms, excessive noise or repetitive physical demands can increase disease or injury risk. Psychosocial factors such as low job control, insecure employment, excessive workload and chronic workplace stress may also affect health. Employment can simultaneously provide income, social connection and access to occupational protections, so the relationship between work and health is complex. Differences in occupational exposure often reflect wider patterns of education, labour-market opportunity, regulation and social class rather than isolated individual decisions.
Healthcare access and quality can contribute to inequalities when populations differ in their ability to obtain timely, effective and appropriate prevention or treatment. Barriers may include distance, transport, cost, appointment availability, language, disability access, digital exclusion, health literacy and difficulties navigating services. Even when services are formally available to everyone, differences in continuity, communication, trust or treatment can affect outcomes. Healthcare is therefore one determinant among many. It can reduce inequalities through prevention and effective treatment, but it cannot completely compensate for unequal exposure to poor housing, poverty, environmental hazards or unhealthy working conditions.
Health behaviours contribute to inequalities but are themselves socially patterned. Smoking, alcohol consumption, diet, physical activity and use of preventive services can differ between populations, but these behaviours are influenced by stress, income, education, commercial marketing, social norms, local environments and availability of alternatives. Describing behaviour as a cause without examining its determinants can therefore produce an incomplete explanation. Behavioural pathways may also mediate relationships between social circumstances and disease. For example, chronic stress or financial insecurity can influence coping behaviours, while limited access to safe recreational space can affect physical activity.
Biological and developmental processes can connect social conditions with later health. Early-life nutrition, maternal health, childhood adversity, exposure to environmental hazards and educational opportunities can influence development and later disease risk. Chronic stress can affect neuroendocrine, cardiovascular and immune systems, although the precise biological pathways differ by condition. Ageing and accumulated exposure can produce additional differences because disadvantage experienced repeatedly over decades may increase vulnerability to disease. Genetic variation can also influence individual susceptibility, but genetic factors generally interact with environmental and social conditions and do not provide a complete explanation for population-level health inequalities.
Health inequalities can also be produced or reinforced by discrimination, social exclusion and unequal distribution of power and resources. Discrimination can affect employment, housing, education, healthcare experiences and exposure to stress, while social exclusion can restrict access to supportive networks and opportunities. Public policy can either widen or narrow inequalities depending on how resources, services, taxation, housing, education, employment protections and healthcare are distributed.
Because determinants operate together, effective approaches often require action at several levels rather than a single intervention. The causes of health inequalities are consequently best understood as a complex system in which socioeconomic conditions, environmental exposures, behaviours, healthcare, social relationships and biological processes interact across the life course.
