WEDNESDAY, Dec. 17, 2025 (HealthDay News) -- Inflammatory bowel disease (IBD) and body mass index (BMI) seem to have a causal effect on the risk for hidradenitis suppurativa (HS), according to a study published online Dec. 10 in JAMA Dermatology.

Rune Kjærsgaard Andersen, M.D., Ph.D., from the Herlev and Gentofte Hospital in Denmark, and colleagues examined the relationship between BMI and smoking and HS and between three inflammatory diseases and HS in a Mendelian randomization (MR) study. The study was conducted on five exposure phenotypes (BMI, smoking, psoriasis, IBD, and systemic sclerosis [SSc]). Large genetic White European cohorts from genome-wide association studies of each of the six phenotypes were used in the MR analyses.

The researchers observed genetic correlations between HS and all exposure phenotypes except SSc. The effect of BMI on HS was supported by MR analyses (β = 0.87; odds ratio per BMI unit, 1.20), with no signs of pleiotropy. A significant causal estimate was seen for smoking, but in subsequent sensitivity analyses, the results became inconclusive. Results supported a causal effect of IBD on HS, without signs of pleiotropy (β = 0.18; odds ratio, 1.20).

"Because none of the sensitivity analyses revealed signs of pleiotropic effects, the MR should be viewed as inconclusive rather than proof of no causal effect," the authors write.

Several authors disclosed ties to biopharmaceutical companies, including Leo Pharma and Novo Nordisk; the Leo Foundation and Novo Nordisk Foundation supported the study.

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