Health inequality refers to measurable differences in health status, health outcomes, exposure to health risks or access to healthcare between individuals or groups. Differences may be observed according to socioeconomic position, geography, occupation, education, disability, ethnicity, sex, age or other characteristics, depending on the context and available evidence. Health inequalities can involve differences in life expectancy, disease prevalence, mortality, disability, mental health, exposure to environmental hazards or use and quality of healthcare. The term is descriptive: it identifies a difference between groups but does not by itself state whether the difference is avoidable, unfair or ethically unacceptable. That distinction is important when differentiating health inequality from health inequity.
Health inequality and health inequity are related but not identical concepts. Inequality generally describes an observed difference, whereas inequity is commonly used to describe differences considered unfair, avoidable or unjust. For example, people living in different geographic areas may have different rates of disease; that is an inequality. Determining whether the difference represents an inequity requires consideration of its causes, avoidability and fairness. Terminology varies between disciplines and countries, and some authors use “health inequalities” broadly to include differences that would elsewhere be called inequities. Precise interpretation therefore depends on context, but the central idea is that health outcomes are not distributed equally across populations.
Health inequalities can be measured using many indicators. Life expectancy at birth estimates average expected lifespan under current mortality conditions, while healthy life expectancy attempts to capture expected years lived in good health. Mortality rates compare deaths between populations using specified denominators, and morbidity measures can quantify disease prevalence or incidence. Measures of deprivation, income, education or occupation can be linked to health outcomes to identify socioeconomic gradients.
Inequalities can also be assessed using absolute differences, such as the difference in mortality rates between two groups, or relative differences, such as ratios or percentage comparisons. Choice of measure can affect the apparent magnitude of an inequality, so both absolute and relative measures may be useful.
A health gradient is a particular pattern in which health changes progressively across levels of socioeconomic position rather than only differing between the poorest and richest groups. The social gradient in health has been observed across many populations and outcomes. People with greater socioeconomic resources often experience longer life expectancy and lower rates of many adverse health outcomes, although the precise pattern differs by condition and population. This gradient demonstrates that health inequality is not limited to an extreme contrast between poverty and affluence. Factors such as education, income, employment, housing, working conditions, neighbourhood environment, social resources and access to healthcare can combine to influence health throughout the social distribution.
Health inequalities can occur in access to healthcare as well as in health outcomes. Groups may differ in whether services are geographically accessible, financially affordable, culturally appropriate, available at convenient times or physically accessible to people with disabilities. Differences can also arise in waiting times, communication, continuity of care, treatment quality and ability to navigate complex healthcare systems. Importantly, equal provision does not always produce equal access or equal outcomes because people have different levels of need and different barriers. Assessing health inequalities therefore requires consideration of both service use and the wider circumstances that influence whether people can benefit from healthcare.
Health inequalities are not restricted to diseases traditionally considered “social”. They can occur in cardiovascular disease, cancer, respiratory disease, infectious diseases, maternal and child health, mental health, injuries and disability. Environmental exposures can contribute, including air pollution, poor housing, noise, unsafe workplaces and limited access to green space. Behavioural factors can contribute but are often shaped by wider conditions. For example, diet, smoking and physical activity are influenced by income, education, stress, commercial environments, social norms and access to safe places for activity. Focusing only on individual behaviour can therefore obscure important upstream determinants.
Health inequalities can change over time. Improvements in average population health do not necessarily reduce inequalities because different groups may improve at different rates. An intervention can produce a large overall benefit while leaving a gap between groups unchanged or, in some circumstances, increasing it if advantaged groups are better positioned to adopt or access the intervention. Conversely, policies addressing housing, income, education, working conditions or healthcare access can affect the distribution of health determinants as well as average health. Monitoring inequalities therefore requires examining outcomes across population groups rather than relying only on national averages.
Understanding health inequality is important for public-health planning, resource allocation and evaluation of interventions. Describing a disparity is only the first step; researchers then investigate mechanisms, distinguish correlation from causation, identify modifiable determinants and assess whether interventions alter the distribution of outcomes. Health inequalities reflect complex interactions among biology, behaviour, environment, social circumstances, economic resources and healthcare systems. They should therefore not automatically be interpreted as evidence of differences in individual responsibility or biology. A population-level difference can emerge from unequal exposure to risks, unequal access to protective resources, cumulative disadvantage across the life course and differences in treatment or prevention opportunities.
