{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T23:35:39Z","timestamp":1791588939602,"version":"4.3.4"},"reference-count":50,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2026,5,8]],"date-time":"2026-05-08T00:00:00Z","timestamp":1778198400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background\/Objectives: Psoriasis and Hashimoto\u2019s 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\u2013skin and gut\u2013thyroid 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\u2019s 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\u2019s 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\u2013producing 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\u2013skin\u2013thyroid 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\u2019s thyroiditis. While microbiome-targeted interventions show biological plausibility, well-designed, mechanistically informed randomized controlled trials are required to establish causality and clinical relevance.<\/jats:p>","DOI":"10.3390\/nu18101501","type":"journal-article","created":{"date-parts":[[2026,5,11]],"date-time":"2026-05-11T20:14:16Z","timestamp":1778530456000},"page":"1501","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["The Gut\u2013Skin and Gut\u2013Thyroid Axis in Autoimmunity: Roles of Dysbiosis, Microbial Metabolites, Immune Dysregulation, and Diet in Psoriasis and Hashimoto\u2019s Thyroiditis"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0009-0000-7627-6423","authenticated-orcid":false,"given":"Sab\u012bna","family":"Riba\u010duka","sequence":"first","affiliation":[{"name":"Faculty of Medicine, Riga Stradi\u0146\u0161 University, LV-1007 Riga, Latvia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6775-841X","authenticated-orcid":false,"given":"Sab\u012bne","family":"Upmale-Engela","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, Riga Stradins University, LV-1007 Riga, Latvia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0286-7228","authenticated-orcid":false,"given":"Ieva","family":"Vaivode","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, Riga Stradins University, LV-1007 Riga, Latvia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ilze","family":"Konrade","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, Riga Stradins University, LV-1007 Riga, Latvia"},{"name":"Department of Endocrinology, Riga East Clinical Hospital, Hipokrata Str. 2, LV-1038 Riga, Latvia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"M\u0101ra","family":"Rone-Kupfere","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Riga Stradi\u0146\u0161 University, LV-1010 Riga, Latvia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,5,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2096995","DOI":"10.1080\/19490976.2022.2096995","article-title":"Impact of Gut Microbiome on Skin Health: Gut-Skin Axis Observed through the Lenses of Therapeutics and Skin Diseases","volume":"14","author":"Mahmud","year":"2022","journal-title":"Gut Microbes"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Polak, K., Bergler-Czop, B., Szczepanek, M., Wojciechowska, K., Fr\u0105tczak, A., and Kiss, N. 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