Associations of palmar surface lactic acid with hand scaling and in vitro pathogen inactivation: A cross-sectional study

The relationship between palmar surface lactic acid and hand scaling is not well understood. This cross-sectional study examined associations between palmar surface lactic acid, hand scaling, and in vitro anti-pathogenic activity, to generate hypotheses relevant to hand skin condition and pathogen inactivation. In 49 healthy adults, after standardized hand washing and acclimation (20°C, 40% RH), we assessed scaling (visual score), surface lactic acid and stratum corneum ceramides (LC–MS), stratum corneum amino acids (ion-exchange chromatography), skin pH and temperature, and sweat rate. Anti-pathogenic activity of palmar extracts was quantified as log 10 reduction against influenza A/H3N2, Escherichia coli NBRC3301, and Staphylococcus aureus NBRC13276. Associations were evaluated using Spearman and partial correlations with Benjamini–Hochberg correction for false discovery rate. Higher lactic acid content was associated with less scaling. Stronger anti-pathogenic activity was also associated with less scaling. Total ceramides and total amino acids were not significantly associated with scaling, whereas several ceramide classes showed negative associations with scaling. In partial correlation models, lactic acid remained independently associated with greater anti-pathogenic activity and with lower scaling (significant in two models and trend-level in one model), and the simple correlation between anti-pathogenic activity and scaling was attenuated after accounting for lactic acid. Lactic acid was also associated with sweat rate across these models (significant in two and trend-level in one). These findings are hypothesis-generating and may inform future mechanistic or interventional studies on lactic acid and palmar skin. Given the cross-sectional design, causality cannot be inferred.