Washed microbiota transplantation relieves atopic dermatitis via gut–skin microbiome rebalancing

BACKGROUND: Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease in which dysbiosis of gut and skin microbiota contributes to pathogenesis and severity. Washed microbiota transplantation (WMT)-an improved form of fecal microbiota transplantation with enhanced safety and microbiota quality control-has shown efficacy in a single reported adolescent case. However, clinical data on WMT in AD and its effects on the skin and gut microbiota remain limited. METHODS: Twenty-three patients with moderate-to-severe AD received at least two courses of WMT between January 2022 and December 2023. Disease activity was evaluated using the SCORing Atopic Dermatitis (SCORAD) index, the Eczema Area and Severity Index (EASI), the Numeric Rating Scale (NRS) for itch, and the Dermatology Life Quality Index (DLQI). Peripheral blood counts, cytokine profiles, lymphocyte subsets, and gut and skin microbiota were assessed before and after treatment. RESULTS: WMT was well tolerated (58 sessions; 5.2% mild adverse events) and significantly improved SCORAD, EASI, DLQI, and NRS scores, with greater EASI reductions in adults than in children. Absolute basophil counts decreased significantly after treatment, whereas other hematologic and cytokine parameters remained stable. Gut microbiota showed an increased Gut Microbiome Health Index, a decreased Microbial Dysbiosis Index, and enrichment of short-chain fatty acid-producing taxa, including the Eubacterium coprostanoligenes group, Lachnospiraceae, and Coprococcus. Skin microbiota shifted from Staphylococcus dominance to higher abundances of Acinetobacter, Perlucidibaca, and other potentially protective genera, inversely correlating with disease severity and systemic inflammation. CONCLUSIONS: WMT appears safe and effective in alleviating clinical manifestations of AD while reshaping both gut and skin microbiota. These parallel microbial shifts support the gut-skin axis as a therapeutic target and highlight WMT as a promising microbiota-centered intervention for immune-mediated skin diseases.