Penicillin (PCN) allergy is the most commonly reportedly drug allergy, and is reported by up to 20% of hospitalized patients.1 The overwhelming majority of these patients are shown to not have true IgE-mediated hypersensitivity reactions when assessed by penicillin skin testing (PST).1 Reported history of PCN allergy has been associated with increased morbidity including longer hospital stays, and increased rates of infection with drug-resistant organisms including C. difficile. This evidence concerns the gene IGHE and Allergy.