Significantly Different Prevalences of Contact Allergy to Hydroperoxides of Linalool and Limonene When Patch Testing With Different Patch Test Chambers

BACKGROUND: The prevalence of contact allergy to linalool hydroperoxides (HPs) and limonene HPs is high and differs in different populations. Patch test techniques might affect the results. OBJECTIVES: To report the prevalence of contact allergy when the HPs were tested in different test chambers. MATERIALS AND METHODS: Consecutive adult dermatitis patients were patch tested during April 2023-July 2024 with linalool HPs and limonene HPs in Finn Chamber (FC), Finn Chamber AQUA (FCA) and IQ Ultra (IQ) chambers simultaneously. RESULTS: In total, 629 patients were tested. For linalool HPs, the highest prevalence was observed in FCA (7.0%), followed by IQ chambers (5.7%) and FC (5.1%) with a significant difference between FCA and FC (p-value = 0.036). Similarly, for the limonene HPs: FCA = 7.8%, IQ = 3.8% and FC = 3.0%, with significant differences between FCA and FC, and between FCA and IQ chambers (both p-values < 0.001). Up to 40% of the doubtful cases in one chamber could become positive when tested with another test chamber. CONCLUSIONS: For both HPs, using different patch test chambers can affect patch test results. A doubtful reaction in one chamber tested might be a weak allergic reaction when tested with other chambers. Contact allergy might be missed.