Most consistently, rosacea has been found to be associated with an increased risk of inflammatory bowel diseases (IBD). This relationship is supported by two 2019 meta-analyses of observational studies and a nationwide cohort study in Denmark.[1][2][3] While the mechanisms underlying this connection are unclear, both disease states involve dysfunction of the immune system and chronic inflammation.[2]
Small intestinal bacterial overgrowth (SIBO) has been suggested by some, but not all, studies to be more common in people with rosacea. Despite these inconsistent findings, treatment of SIBO with the antibiotic rifaximin has been found in multiple trials to improve symptoms of rosacea, with effects persisting for months to years.[4][5][6]. Rifaximin acts locally in the gut, and is not thought to influence systemic inflammation, unlike the other antibiotics used in rosacea management.[6]
Rosacea may be associated with an increased risk of celiac disease, and this relationship is further supported by a genome-wide association study that found that rosacea and celiac disease share two genetic risk markers.[6]
While H. pylori infection has been suggested to contribute to rosacea, this is controversial and not strongly supported by the evidence. One meta-analysis of observational studies reported a small, but not statistically significant, positive association between rosacea and H. pylori infection, while another meta-analysis of observational studies and a nationwide cohort study did not find a significant relationship. Any improvement in rosacea symptoms following treatment for H. pylori infection could, in theory, be attributed to the anti-inflammatory effects of the antibiotics.[7][3][6]