Background/Objectives: Psoriasis and Hashimoto’s thyroiditis are chronic immune-mediated disorders affecting distinct target organs but sharing overlapping pathogenic mechanisms, including gut dysbiosis, impaired intestinal barrier function, and systemic immune dysregulation. Growing evidence highlights the gut–skin and gut–thyroid axes as important interfaces linking microbial alterations to immune-mediated inflammation. This review aims to synthesize current knowledge on gut microbiota alterations in psoriasis and Hashimoto’s thyroiditis, with particular emphasis on intestinal permeability, immune pathways, and microbiome-derived metabolites. Methods: A narrative review of experimental and human observational studies was conducted to evaluate evidence on gut microbiota composition, intestinal barrier integrity, immune regulation, bile acid metabolism, and dietary influences in psoriasis and Hashimoto’s thyroiditis. The relevant literature examining mechanistic pathways and clinical associations was included. Results: Both conditions are associated with altered gut microbial composition, including reduced abundance of short-chain fatty acid–producing taxa, which may impair epithelial barrier integrity and promote systemic immune activation. Increased intestinal permeability and enhanced Th17-driven inflammatory responses are reported in both diseases. Recent studies suggest that dysregulated bile acid metabolism may influence intestinal permeability and immune balance along the gut–skin–thyroid axis, although direct clinical data remain limited. Dietary patterns, particularly anti-inflammatory and Mediterranean diets, are consistently associated with increased microbial diversity, improved metabolic profiles, and reduced systemic inflammation. However, most human evidence is observational. Conclusions: The gut microbiome represents a potential mechanistic link connecting diet, intestinal barrier function, immune regulation, and organ-specific autoimmunity in psoriasis and Hashimoto’s thyroiditis. While microbiome-targeted interventions show biological plausibility, well-designed, mechanistically informed randomized controlled trials are required to establish causality and clinical relevance.

The global rise in antimicrobial resistance has spurred increased interest in alternative antimicrobial agents, particularly essential oils (EOs). These oils are complex mixtures of volatile compounds that exhibit documented biological activity. This study evaluated antimicrobial and antibiofilm effects of selected EOs against clinically relevant bacterial and fungal pathogens. Antimicrobial activity against planktonic cells was assessed using disc diffusion assays with DMSO-diluted EO solutions against Escherichia coli (E.coli), Staphylococcus aureus (S.aureus), Pseudomonas aeruginosa, Klebsiella pneumoniae, and Candida albicans. Antibiofilm activity of E. coli and S. aureus was examined using ethanol-based EO formulations, with biofilm viability quantified by colony forming unit (CFU) enumeration. Cinnamon (Cinnamomum verum) oil showed the strongest and most consistent activity, inhibiting planktonic and biofilm models. Tea tree (Melaleuca alternifolia), lemongrass (Cymbopogon citratus), rosemary (Rosmarinus officinalis), rose (Rosa damascena), and jasmine (Jasminum officinale) oils showed significant planktonic antimicrobial effects, while jasmine oil (Jasminum officinale) demonstrated pronounced antibiofilm activity against S. aureus, including strong biofilm eradication in several replicates. In contrast, chamomile (Matricaria chamomilla) and sandalwood (Santalum austocaledonicum) oils showed limited or no activity. These findings highlight differences between planktonic and biofilm responses, emphasizing the importance of incorporating biofilm models into antimicrobial evaluation. Overall, Cinnamomum verum and Jasminum officinale oils may serve as complementary antimicrobial agents, warranting further investigation.