What is sodium metabisulphite (metabisulfite)?
Sodium metabisulphite (sodium metabisulfite, sodium pyrosulphite, disodium metabisulphite) is an inorganic compound used as a disinfectant, antioxidant, preservative, bleaching agent, and stabiliser in medications.
It can induce an allergic reaction in humans who are sensitive to sulphites (sulfites), including Type I reactions (anaphylaxis, urticaria, bronchospasm, and gastrointestinal symptoms) and type IV reactions such as allergic contact dermatitis. These reactions may also co-occur.
Where is sodium metabisulphite found?
- Food preservatives in items such as jams, baked products, potato chips, dried fruits, fruit juices, and pickled foods
- Preservative/stabiliser in certain medications; for example, medicines that contain adrenaline, anaesthetics, paracetamol, antifungals, corticosteroids, haemorrhoidal creams, and eye drops
- Fungicides and antimicrobials used during the shipping of foods or clothing
- Sanitising equipment used in some industrial processes and wastewater treatment
- Corrosion inhibitors in the oil industry or rust-stain remover
- Photographic chemicals
Occupational exposure may involve:
- Food and beverage industry/handlers
- Medical professionals (e.g. nurses)
The most common sources of exposure are personal products (most frequently hair dyes and cosmetic products) and medications.
Who gets a contact allergy to sodium metabisulphite?
Approximately 1.4–4.5% of individuals may have a positive reaction, where allergy to sodium metabisulfite is an increasingly recognised cause of allergic contact dermatitis.
What are the features of contact allergy to sodium metabisulphite?
Sensitised individuals will develop contact dermatitis on exposure.
The most common primary site of the allergic reaction are the hands and face. The rash can be red, swollen, and vesicles or blisters may develop.
Individuals may also develop systemic reactions to disodium metabisulphite after ingestion, as sulphites can occur naturally in some foods and beverages, and may be added as preservatives. These systemic reactions are rare, but oral intake of sodium metabisulfite in dietary products or medication may be sufficient to cause symptoms such as erythema of intertriginous areas or a more generalised eczematous rash.
How is contact allergy to sodium metabisulphite diagnosed?
Patch testing confirms the diagnosis. Those sensitised will develop a positive result; tests are read 48 and 96 hours after application of the allergen.
How is contact allergy to sodium metabisulphite treated?
Products containing the allergen must be discontinued and avoided. The dermatitis is treated by the application of a topical steroid until the reaction settles.
See allergic contact dermatitis for further information on treatment.
What should I do to avoid sodium metabisulphite?
It is essential to avoid products that contain the offending parent allergen (sodium metabisulphite), which may appear in the individual constituents list on the product label or insert. Product manufacturers’ websites usually have a tab that reveals the list of individual constituents, and this is often much easier to read than the fine print on the package label.