Independent and Combined Effects of Household Solid Fuel Use and Outdoor PM2.5 on Mental Health among Reproductive-aged Women in Low- and Middle-Income Countries

Air pollution is a critical public health challenge in low- and middle-income countries (LMICs), disproportionately affecting women of reproductive age who are often exposed to both household air pollutions (HAP) from biomass fuel combustion and ambient air pollution (AAP). This study quantified the independent and combined effects of HAP and AAP on mental health severity among women of reproductive age. Utilizing nationally representative data from the 2022 and 2022–23 Demographic and Health Surveys (DHS), we analyzed a sample of 19,932 women aged 15–49 years across two LMICs: Mozambique, and Nepal. Mixed-effect regression models were employed, adjusting for sociodemographic, behavioral, and health-related confounders. We found that household solid fuel use was significantly associated with a 4.74% increase in PHQ-9 scores (95%CI: 0.56%−9.08%, p  = 0.025). Each 5 µg/m³ increase in PM₂.₅ concentration was associated with a 1.22% increase in GAD-7 scores for 30-day exposure (95%CI: 0.44%−2.01%, p  = 0.002), a 1.52% increase for 90-day exposure (95%CI: 0.60%−2.44%, p  = 0.001), and a 1.32% increase for 365-day exposure (95%CI: 0.07%−2.58%, p  = 0.038). We observed significant synergistic interactions between HAP and AAP, with solid fuel use consistently amplified the effects of PM₂.₅ exposure for increase in PHQ-9 (interaction p  = 0.0338) and GAD-7 scores (interaction p  < 0.05). However, no significant additive interaction was observed. Sensitivity analyses confirmed robustness after excluding pre-existing mental health conditions. This study highlights the dual burden of household and ambient air pollution on women’s mental health in LMICs, emphasizing the need for targeted interventions—such as clean energy transitions—to mitigate these risks. Graphical Abstract