The External Exposome and Life Expectancy: Formaldehyde as a Leading Predictor in U.S. Counties

Life expectancy in the United States varies significantly by region, a gap often explained by socioeconomic factors like income and education. However, the relative contribution of atmospheric exposures is less understood. We identify formaldehyde exposure and wet-bulb temperature as leading predictors of county-level life expectancy. Our analysis of over 24,000 county-year observations (2012–2019) reveals that formaldehyde consistently ranks as the second-strongest predictor of life expectancy, surpassed only by educational attainment. Wet-bulb temperature, a physiological measure of heat stress, emerges as a top-five predictor. We identified these patterns using XGBoost with SHAP analysis, integrating atmospheric, livestock, and socioeconomic data within an external exposome framework. These results suggest that air pollutants and heat stress capture health-relevant information beyond traditional socioeconomic indicators.