Understanding the compound risk of heat, humidity and air pollution on human health: A scoping review

This scoping review searched five online databases – four for peer-reviewed literature (Medline, Excerpta Medica dataBASE (EMBASE), Scopus and Global Index Medicus (GIM)) as well as one grey literature site (ReliefWeb) – using prearranged keywords combining compound exposures of air pollution, extreme heat, humidity and a health outcome. A total of 506 papers matched our search criteria of which 33 were included in the final synthesis. 

Overall, the papers found worse health outcomes during periods that coincided with compound exposure for mortality, cardiovascular conditions, respiratory and pulmonary conditions, kidney function, birth complications, and physiological or cognitive functions. It is clear that although the health risks of air pollution, heat and humidity are well established individually, evidence on compound risks is lacking. This paper emphasizes that a more complex understanding of heat is necessary, including an assessment of the compound effect of humidity with temperature and air pollution.

According to the authors, increased effort should be made to expand the scope of heat and air pollution research to include:

1. higher granularity and quality of meteorological and air quality data to better assess individual risk levels;
2. health outcomes beyond cardio-respiratory mortality and morbidity;
3. broader geographical scope of research into understudied regions e.g., the Middle East and North Africa (MENA);
4. evaluations of earlier health–heat mitigation and adaptation interventions.