Contact allergy to sodium sulfite and its relationship to sodium metabisulfite

Background. Sulfites are in widespread use as preservatives/antioxidants. There is increasing recognition of allergic contact dermatitis caused by sodium metabisulfite; however, contact allergy to sodium sulfite is less well recognized. Objectives. We sought to establish the prevalence of positive patch test reactions to sodium sulfite in our patient population and investigate its relationship with sodium metabisulfite. Methods. Over a 4‐month period, 183 patients referred for patch testing were tested with sodium sulfite 1% pet. in addition to sodium metabisulfite 1% pet., which already forms part of our baseline series. Results. Positive allergic reactions occurred to sodium metabisulfite in 5.5% of the tested patients and to sodium sulfite in 3.8% of the tested patients. Sixty per cent of patients with a positive reaction to sodium metabisulfite were positive to sodium sulfite. Only 1 patient (0.6%) with a negative reaction to sodium metabisulfite showed a positive reaction to sodium sulfite. Conclusions. This study shows that the majority of patients with positive reactions to sodium metabisulfite are also positive to sodium sulphite. Routinely patch testing with sodium sulfite is probably unnecessary, as most patients with positive reactions will also react to sodium metabisulfite. Clinicians should consider advising patients to avoid sodium sulfite and other sulfites when a positive allergic reaction to sodium metabisulfite occurs.