The association between personal hygiene and mental health, and the modifying roles of the universal health coverage index in children and adolescents: a comparative analysis from multiple countries

Background: Personal hygiene and mental health are both core determinants of adolescent well-being, yet their interplay and the modifying role of national health system coverage remain largely unexplored in cross-national populations. Therefore, we aimed to investigate associations between personal hygiene behaviours and mental health outcomes in adolescents and the modifying factors of the universal health coverage (UHC) index across multiple countries. Methods: We analysed data on 153,413 adolescents aged 12-17 from 51 countries collected through the Global School-based Student Health Survey between 2013 and 2019. Self-reported hygiene behaviours included toothbrushing and handwashing, and mental health outcomes included suicide ideation, bullying, being lonely, worry-related sleep disorders, and having no close friends. We examined associations using binary logistic regression models, stratified by sex and UHC index groups. Results: We found that all four hygiene behaviours were generally associated with improved mental health outcomes in boys and girls (P < 0.001). For boys, differences between UHC groups in hygiene scores were associated with mental health outcomes, particularly with suicide ideation (lower UHC: odds ratio (OR) = 0.88; 95% confidence interval (CI) = 0.85-0.91; higher UHC: OR = 0.82; 95% CI = 0.79-0.85), bullying (lower UHC: OR = 0.84; 95% CI = 0.82-0.86; higher UHC: OR = 0.78; 95% CI = 0.76-0.80), being lonely (lower UHC: OR = 0.91; 95% CI = 0.89-0.93; higher UHC: OR = 0.88; 95% CI = 0.86-0.90), and having no close friends (lower UHC: OR = 0.82; 95% CI = 0.79-0.85; higher UHC: OR = 0.77; 95% CI = 0.74-0.80). For girls, higher hygiene scores were only associated with lower odds of being lonely in UHC groups, with a significant difference between groups (lower UHC: OR = 0.88; 95% CI = 0.86-0.90; higher UHC: OR = 0.81; 95% CI = 0.79-0.83, P-value for difference ≤0.001). Conclusions: Our analysis indicates that individual hygiene practices are associated with reduced risks of adverse mental health outcomes in adolescents. The UHC index seems to play a modifying role in this context, with amplified associations in higher UHC coverage countries, particularly for boys.