Hypersensitivity of azo dyes in urticaria patients based on a single-blind, placebo-controlled oral challenge

INTRODUCTION: The role of azo dyes in urticaria is not fully understood. AIM: To assess the incidence rate of hypersensitivity reactions to food azo dyes based on a placebo-controlled oral challenge in a group of patients with suspected urticaria exacerbation after consuming food additives. MATERIAL AND METHODS: The study included patients over 18 years of age with chronic urticaria, in whom hypersensitivity to food additives was suspected based on a questionnaire and medical history. Patients suspected of urticaria exacerbations after ingestion of azo dyes were enrolled in a placebo-controlled single-blind oral challenge (OC) with a mixture of azo food dyes: tartrazine, Quinoline Yellow, Sunset Yellow, Cochineal Red, Allura Red, and azorubine. RESULTS: Out of 110 patients (76 women and 34 men, mean age 46.1 (20–76 years), 39 patients were qualified for the oral challenge. We observed two subjects (5.1%) with a positive result. CONCLUSIONS: Azo dyes ingested in food or medications incidentally cause urticaria but may exacerbate its course. Oral challenge-confirmed hypersensitivity to azo dyes is much less common than reported by patients.