Reliability of Expired Allergens in Patch Testing: A Comparative Study With Non-Expired Series

Patch testing remains the gold standard in the diagnosis of allergic contact dermatitis. Patches used in testing consist of a wide spectrum of allergens, with variability in the stability of products over time. Due to limited allergen stability, careful storage and preparation is needed to prevent product degradation over time. Expiration dates are provided by manufacturers to ensure stability and reactivity, while minimizing the risk of product degradation contributing to inaccurate testing results. Preparation of patch series can be time intensive and procurement of allergens comes with an associated economic burden. Expired allergens are not routinely used in patch testing, however many clinics have expired allergens accessible. There is paucity of evidence comparing the reactivity of expired vs non-expired patch series. If expired allergens remain effective, this could result in significant cost-savings and accessibility implications for dermatology practice.

Inclusion Criteria: * Adults (age 18 years or older) referred for patch testing. Exclusion Criteria: * Relative or absolute contraindication to patch testing * Wide spread dermatitis prior to patch placement * Inability to return to clinic for reading of results * Patient non-consenting