Sodium Metabisulphite Contact Allergy: Think Wine and Food!

Background Sodium metabisulphite (SMBS) is a known contact hapten in beverages, foodstuffs, hair dyes, topical and systemic medications, and cosmetics. Objectives To investigate SMBS contact allergy in our tertiary referral patch testing clinics. Methods A retrospective audit was performed of 1367 patients patch tested to 1.0% SMBS in petrolatum between 1/1/2014 and 31/12/2023, and added to the Australian Baseline Series in 2020. Relevance was assessed by consultant dermatologists. Results 87/1367 (6.4%) patients patch tested to SMBS had a positive reaction; 24/87 (27.6%) of these reactions were relevant. No cases were occupational. Eight (33.3%) cases presented with oral lichen planus (OLP) whilst four (16.7%) presented with allergic contact cheilitis (ACC). Overall, 19 (79.2%) patients had facial, oral or lip‐related involvement. The most common exposure sources were alcoholic beverages (12 patients, 50%), mostly wine, and foodstuffs (10 patients, 41.7%), mostly dried fruits. Eight patients had more than one source of exposure. However, patients often reacted to multiple haptens, so other factors may have contributed. Conclusion SMBS contact allergy is not uncommon, but relevance can be difficult to ascertain. OLP, ACC, and facial rashes predominated. Wine and foodstuffs were the most important sources of exposure. SMBS should be included in baseline patch series.