Introduction
Products containing sulphites
Demographics
Causes
Clinical features
Variation in skin types
Complications
Diagnosis
Differential diagnoses
Treatment
Prevention
Outcome
Sulphites (US spelling, sulfites) are inorganic compounds that are widely used commercially for their antioxidant, preservative, bleaching, disinfectant, and stabilising properties. Sulphites also naturally occur at low levels in some foods eg, fermented foods and beverages.
Due to the increasing frequency of allergic reactions to sulphites, they were named the ‘Allergen of the Year’ by the American Contact Dermatitis Society (ACDS) in 2024.
It should be noted that sulphites are distinct from sulphates, and they do not cross-react. The latter are not usually allergenic and do not cause reactions in individuals sensitive to sulphites.
Sulphites come in several forms, including:
Sulphites are commonly used in food and beverage, pharmaceutical, and personal care products:
Industry |
Role of sulfites |
Examples |
|---|---|---|
Food and beverages |
Preservative and antioxidant
|
|
Personal care products |
Preservative |
|
Pharmaceuticals |
Stabiliser and preservative in some medications |
|
Other |
|
|
Occupational exposure may include:
Any individual exposed to sulphites can become sensitised and develop an allergy. This may occur in occupational settings such as in those listed above.
Patients with impaired barrier function of the skin are more prone to allergic contact dermatitis.
Sulphites can induce an allergic reaction in people who are sensitive to them. This can be an acute (type I) hypersensitivity reaction (urticaria, asthma, anaphylaxis] or a delayed (type IV) hypersensitivity reaction. Both types of reactions can co-occur.
Contact allergies to sulphites are caused by delayed hypersensitivity reactions (T-cell mediated).
In sensitised individuals, skin exposed to sulphites will develop dermatitis/eczema. This reaction usually occurs 48-72 hours after contact. The rash is typically red and can be scaly, itchy, and swollen. In moderate to severe reactions, they can develop vesicles or blisters.
Commonly affected areas include the face, lips, and hands, but any part of the body that comes into contact with sulphite-containing products can develop dermatitis.
If sulphites are ingested, a sensitised individual may also develop systemic contact dermatitis, though this is rare.
In people with darker skin types, erythema may not be an obvious feature and rashes may instead appear brown, purple, or grey.
Patch testing is the gold standard test to confirm an allergic contact dermatitis.
Sulphites are usually tested in the form of sodium metabisulphite, which is one of the allergens in the New Zealand and Australian Baseline Series.
Sulphite exposure can also cause irritant contact dermatitis and contact urticaria.
Depending on the clinical presentation, other differential diagnoses include:
Once sulphites have been identified as an allergen, sulphite-containing products must be discontinued and avoided.
Active dermatitis is treated in the standard way as with other types of dermatitis.
For more information, see allergic contact dermatitis.
Product labels should be checked thoroughly for their ingredients to avoid those containing sulphites. Sulphites must be declared on the label of a packaged food when present in concentrations of 10 mg/kg or more. They may appear on the label under a code or by their various forms such as sodium metabisulphite, sulphur dioxide, sodium sulphite, sodium bisulphite, calcium sulphite, or potassium bisulphite.
Symptoms of allergic contact dermatitis usually settle once the allergen is identified, avoided and sufficient treatment is provided.
