Shaping hormones, shaping health On the role of sex steroid hormones and host-microbe interactions

Oral health depends on a dynamic ecological balance between host and microorganisms, in which the oral microbiome contributes to key biological functions. When this balance is disrupted, dysbiosis may occur, increasing the risk of oral diseases such as caries and periodontal disease and potentially contributing to systemic conditions. Among the host factors influencing this ecosystem, sex steroid hormones (SSH)—including estrogens, androgens, and progestagens—have emerged as modulators of oral health.
This thesis investigated how SSH influence host–microbe interactions in the oral cavity and whether hormonal changes have measurable clinical consequences. A series of literature reviews established the theoretical framework, highlighting that the oral cavity is a target organ for SSH and that several oral microorganisms can react to and/or metabolize SSH. This suggests an active role of SSH on both oral microorganisms and oral tissues. Experimental in vitro studies using saliva-derived microcosm biofilms showed minimal direct effects of SSH on multispecies biofilms. Additional in vitro experiments using gingival cells, demonstrated that these hormones can influence gingival epithelial wound healing.
To examine clinical relevance, a longitudinal study followed transgender individuals initiating gender-affirming hormone therapy for one year. While most clinical parameters remained stable, transient changes in gingival inflammation, dry-mouth symptoms, salivary antimicrobial proteins, and microbial composition were observed. Advanced multivariate analysis indicated that the most pronounced adaptations occurred between three and six months after treatment initiation.
Overall, these findings highlight SSH as modulators of oral host–microbiome interactions and emphasize the dynamic interdependence between host, microbes, and environment.