Association between Secondhand Smoke Exposure and Ocular Microbiome Changes in Children

Purpose To investigate whether secondhand smoke (SHS) exposure alters the ocular surface microbiome (OSM) in children and to explore potential functional consequences. Methods 432 children aged 3-18 years were enrolled, including 111 SHS-exposed and 321 unexposed controls. Conjunctival swabs were collected and analyzed by 16S rRNA gene sequencing targeting the V3-V4 region. Sequencing data were processed with Qiime2 and DADA2, and taxonomic classification was based on the SILVA 138 database. Alpha diversity and beta diversity were compared using t-tests and PERMANOVA. Differentially abundant taxa were identified using LEfSe, and predicted functional pathways were analyzed using PICRUSt2 with MetaCyc and KEGG annotation. Results SHS-exposed children showed significantly altered alpha diversity (Chao1, Shannon, Simpson) and distinct beta diversity compared with controls. LEfSe analysis revealed enrichment of several phyla and genera, including Lactobacillus and Rubellimicrobium in controls, with no taxa enriched in SHS-exposed children. Functional prediction showed enrichment of metabolism pathways such as L-methionine salvage, biphenyl, heparin, and toluene degradation and immune-related pathways, including complement activation, T and B cell receptor signaling, MAPK, and TGF-beta pathways. Conclusion SHS exposure in children is associated with significant alterations in ocular surface microbial diversity, community structure, and predicted functional pathways related to environmental stress and immune signaling. These findings highlight the sensitivity of the pediatric OSM to SHS exposure and underscore the importance of minimizing environmental tobacco smoke to protect children’s ocular health.