What does the gut microbiome look like in people with psoriasis?
People with psoriasis consistently have a less diverse and differently composed gut microbiome compared to healthy individuals. A 2022 case-control study using advanced shotgun sequencing found that psoriasis patients had significantly lower microbial richness (p=0.007) and a different community composition (p=0.01) than matched healthy controls [6]. This pattern held even when comparing patients to their own healthy cohabitant partners, ruling out shared environment as the cause [6]. The same study also found that the functional potential of the microbiome — what the bacteria can do — was reduced in psoriasis patients [6].
Specific bacterial groups are consistently different. Two large Mendelian randomization studies (which use genetics to test cause-and-effect) identified several bacteria with a likely causal role. One study of over 770,000 people found that higher levels of the bacterial class Mollicutes and the phylum Tenericutes increased psoriasis risk, while higher levels of the family Victivallaceae and certain Eubacterium groups were protective [1]. Another study confirmed that the genus Eubacterium fissicatena group was protective (odds ratio 0.83), while the family Veillonellaceae increased risk (odds ratio 1.16) [3]. These findings from different populations and methods agree on the direction of effect for several bacteria, strengthening the case for a real biological link.
Can gut bacteria actually cause or worsen psoriasis symptoms?
Yes, experiments show that gut bacteria from psoriasis patients can directly worsen skin inflammation. In a 2021 study, researchers transplanted fecal microbes from psoriasis patients into mice and then induced a psoriasis-like skin condition. The mice that received the psoriasis microbes took significantly longer to recover and had higher levels of the inflammatory molecule IL-17A compared to mice that received healthy microbes or no transplant [2]. This is strong evidence that the gut microbiome is not just a bystander — it actively influences the severity of skin inflammation.
Further supporting a causal role, two large genetic analyses (Mendelian randomization studies) found that certain gut bacteria have a statistically significant causal effect on psoriasis risk [1][3]. These studies use genetic variants as natural experiments to rule out reverse causation (where psoriasis changes the gut) and confounding factors. The fact that both studies, using different datasets and methods, identified overlapping bacterial groups (like Eubacterium fissicatena group) with consistent protective effects makes the case for causality much stronger than observational studies alone.
Can improving gut health help treat psoriasis?
Emerging evidence suggests that treatments targeting the gut microbiome can improve psoriasis symptoms. A 2025 systematic review concluded that probiotics and prebiotics are useful tools for managing psoriasis and atopic dermatitis, working through the gut-skin axis [4]. Another 2024 systematic review of various psoriasis treatments (biologics, conventional drugs, phototherapy, and probiotics) found that favorable treatment outcomes were consistently associated with shifts in the gut microbiome toward a healthier profile [7].
However, the relationship is complex. A 2026 study on the biologic drug secukinumab found that while it dramatically improved skin symptoms after 24 weeks, the gut microbiome changes lagged behind — suggesting that skin improvement can happen before the gut fully recovers [5]. This means that while the gut is involved, it may not be the only driver. Additionally, a 2022 study on methotrexate therapy found that patients who responded poorly had different baseline gut bacteria and blood metabolites, hinting that the microbiome could help predict who will benefit from which treatment [8]. Overall, the evidence supports microbiome-based interventions as a promising complementary strategy, but more research is needed to standardize protocols and identify which specific bacterial changes are most beneficial.
About These Sources
This answer is built on 8 peer-reviewed studies — published from 2021 to 2026, 4 from 2024 or later, 4 in Q1 journals, collectively cited 102 times — selected as the most relevant from 12 studies that passed quality screening, drawn from 52 papers retrieved from a database of over 500 million.
Sources used in this answer
Assessing causal relationships between gut microbiota and psoriasis: evidence from two sample Mendelian randomization analysis
Using Mendelian randomization in over 770,000 individuals, this study found eight specific gut bacterial traits (e.g., Mollicutes, Tenericutes, Victivallaceae, Eubacterium groups) with statistically significant causal relationships to psoriasis risk, some protective and some risk-increasing.
Involvement of Gut Microbiota in the Development of Psoriasis Vulgaris
In a clinical and mouse-model study, 85.5% of psoriasis patients reported gastrointestinal symptoms vs. 58.1% of controls; mice receiving fecal transplants from psoriasis patients showed slower recovery and higher IL-17A levels, directly demonstrating that psoriatic gut microbes worsen skin inflammation.
Psoriasis and gut microbiota: A Mendelian randomization study
A Mendelian randomization study using GWAS data from over 373,000 people confirmed causal relationships for three bacterial groups: Veillonellaceae (increased risk), Candidatus Soleaferrea (increased risk), and Eubacterium fissicatena group (protective).
Gut microbiota-skin axis in the treatment of psoriasis and atopic dermatitis with the promotion of gut health: a systematic review
A 2025 systematic review of 17 studies concluded that the gut microbiota has a major metabolic role along the gut-skin axis, and that probiotics and prebiotics are effective tools for managing psoriasis and atopic dermatitis.
Alterations of the Gut Microbiome in Psoriasis before and after Treated with Secukinumab.
In a study of 110 psoriasis patients treated with secukinumab for 24 weeks, skin symptoms improved significantly, but gut microbiome changes occurred more slowly, suggesting a lag between skin and gut recovery.
Patients with psoriasis have a dysbiotic taxonomic and functional gut microbiota*
In a case-control study using shotgun metagenomic sequencing of 126 samples, psoriasis patients had significantly lower microbial richness (p=0.007), different community composition (p=0.01), and reduced functional richness compared to matched healthy controls and cohabitant partners.
Modulation of the skin and gut microbiome by psoriasis treatment: a comprehensive systematic review.
A 2024 systematic review of psoriasis treatments (biologics, conventional drugs, phototherapy, probiotics) found that favorable outcomes were consistently associated with microbiome shifts toward a healthy profile, supporting microbiome modulation as a therapeutic strategy.
Association of the characteristics of the blood metabolome and gut microbiome with the outcome of methotrexate therapy in psoriasis
In a study of 15 psoriasis patients treated with methotrexate, baseline gut microbiome and blood metabolome features predicted treatment response; good responders showed more microbial activity and less fatty acid biosynthesis after treatment, suggesting the microbiome is involved in drug efficacy.