Anti-IL-23 monoclonal antibodies have been in wide clinical use for over a decade and generally considered safe, with mostly benign side effects including nasopharyngitis, upper respiratory tract infection, and injection site erythema.13 Antibiotic exposure is the most important predisposing factor for C. difficile infection and anti-IL-23 monoclonal antibodies could spare patients from developing further antimicrobial resistance and microbiome disruption. Here, IL37 is linked to Erythema.