Contact allergy to chlorhexidine in a tertiary dermatology clinic in Denmark

Summary Background Chlorhexidine is a widely used disinfectant in the healthcare setting and in cosmetic products. A high prevalence of chlorhexidine contact allergy was reported in Denmark in the 1980s (2.0–5.4% of patients patch tested). It is unknown whether the prevalence is still high, which products cause the contact allergy, and whether accidental re‐exposure occurs in some patients. Objectives To estimate the prevalence of chlorhexidine contact allergy in a tertiary dermatology clinic in Denmark; to investigate whether patch testing with both chlorhexidine diacetate and chlorhexidine digluconate is necessary; to investigate how many patients have combined immediate‐type allergy and contact allergy; and to identify which products cause chlorhexidine contact allergy, and whether patients are accidentally re‐exposed. Methods This was a retrospective study including all patients patch tested with chlorhexidine during 2003–2013 at the Department of Dermato‐Allergology at Copenhagen University Hospital Gentofte (n = 8497). All patients with a positive patch test reaction to chlorhexidine were sent a questionnaire comprising questions about the cause of the allergy and re‐exposure. Results Overall, 1.0% (n = 82) of all patients patch tested with chlorhexidine were positive. A decrease in the prevalence was observed over time, most likely because of lowering of the test concentration from 1.0 to 0.5% in 2008. Of the 82 patients, 28 (0.3%) had positive test reactions to both chlorhexidine salts, 43 (0.5%) had a positive test reaction only to chlorhexidine diacetate, and 11 (0.1%) had a positive test reaction to chlorhexidine digluconate. Three patients were both patch test‐positive and prick test‐positive. A known cause of the allergy was reported by 19 patients (40%) in the questionnaire: the products used in the healthcare setting were mainly reported, but some reported cosmetic products. Accidental re‐exposure was reported by 15 patients (32%), of whom 13 reported symptoms. Conclusions The prevalence of chlorhexidine contact allergy does not seem to be higher in Denmark than in other European countries. Patch testing with both chlorhexidine diacetate and chlorhexidine digluconate may be beneficial. Testing for immediate‐type allergy in patients with a positive patch test reaction to chlorhexidine is recommended. Chlorhexidine‐containing products used in the healthcare setting and in cosmetics are potential causes of sensitization and allergy. Re‐exposure