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.