AbstractBackgroundProphylactic vaccination against influenza and other epidemic viruses is recommended for citizens above 65 years. Several vaccines may contain traces of formaldehyde and are contra‐indicated in patients hypersensitive (in the broadest possible meaning) to formaldehyde. Thorough knowledge on the various subtypes of hypersensitivity is sparse among non‐dermatologists and non‐allergists, and therefore many patients are prevented from vaccination based on a positive patch test to formaldehyde. The purpose of this retrospective study was to investigate whether patients with positive patch test to formaldehyde subsequently receiving a formaldehyde‐containing vaccine and developed a severe adverse reaction.Methods/MaterialsFrom January 2000 to June 2021, 169 patients (>50 years) had a positive formaldehyde patch test at the Department of Dermatology and Allergy Center, Odense University Hospital and were included into this retrospective study. The electronic medical record was assessed for receipt of a formaldehyde‐containing vaccine after patch test and for subsequent contact with the Acute Ward in the Region of Southern Denmark within 14 days after vaccination.ResultsOf the 158 patients residing in the Region of Southern Denmark, 130 patients were vaccinated with one or more formaldehyde‐containing vaccines of whom 123 received an influenza vaccine. No contacts to the acute wards were identified.DiscussionAlthough prospective studies would be beneficial, patients with positive patch test to formaldehyde can be safely vaccinated with formaldehyde‐containing vaccines.