Sulphites

Sulphites are preservatives and bleaching agents used in many foods, drinks and even medicines and cosmetics. For most people they are harmless, but some develop sensitivity reactions that can feel very similar to allergy and occasionally be serious.

What are sulphites?

The term sulphites covers substances such as sulphur dioxide and sodium or potassium metabisulphite. They occur naturally in some foods and are widely added to slow spoilage and lighten colour.

Most reactions to sulphites are sensitivities rather than classic IgE allergies. This means the immune system is not directly involved, but symptoms can still be severe, especially affecting breathing. Sulphite sensitivity is more common in people with asthma.

How can sulphites cause reactions?

• Inhaling sulphur dioxide released from foods may irritate airways.
• They may affect the parasympathetic nervous system, tightening airways.
• Some people have low levels of sulphite oxidase enzyme, leading to build‑up of sulphites.
• They may trigger chemical release such as histamine, prostaglandins or leukotrienes.

There is no single cause — symptoms vary from person to person.

Symptoms

• Wheezing, tight chest, cough
• Hives or rash
• Stomach pain or vomiting
• Worsening eczema

Diagnosis

There are no standard blood or skin tests. Diagnosis relies on medical history and may involve supervised exclusion and reintroduction diets, or carefully controlled “challenge” tests at a clinic, sometimes with lung function monitoring.

Treatment and management

The main management is avoidance. Antihistamines usually do not help sensitivity reactions. If you have asthma, keeping it well controlled is especially important. In rare cases of suspected true allergy, adrenaline may be prescribed.

Avoiding sulphites

Sulphites are one of the 14 major allergens in UK law. They must be listed on labels if added at more than 10 parts per million. Always check labels, as ingredients change. When eating out, ask directly about sulphites — caterers must be able to tell you if foods contain them.

Hidden sulphites

Sometimes sulphites are present in tiny amounts (under 10 ppm) where used as bleaching agents. Common examples include:

• White flour
• Frozen chips
• Crisps
• Fruits used for jam

Which foods and drinks can contain sulphites?

• Processed meats such as sausages and burgers
• Soft drinks, cordials, fruit juices
• Dried fruits and vegetables
• Wine, beer and cider
• Pickles, vinegar and relishes
• Guacamole and dehydrated onions
• Glacé or maraschino cherries
• Coconut milk, salad dressings
• Pre‑cut or frozen potatoes
• Prawns, tofu and bean curd

Medicines

Some medicines contain sulphites, including adrenaline auto‑injectors (AAIs), paracetamol tablets, dental anaesthetics, antibiotics, antifungals, corticosteroid creams and injections, and eye drops. If you are prescribed a medicine or treatment, tell your healthcare team you are sensitive to sulphites. If prescribed adrenaline for allergy, you should still use it in an emergency — the benefit outweighs any risk from sulphite in the injector.

Cosmetics

Sulphites can also appear in cosmetics and toiletries such as:

• Hair dyes and sprays
• Tanning lotions
• Face creams and body washes
• Perfumes and bronzers

Important to know

• If you think sulphites cause symptoms, see your GP.
• Most reactions are sensitivities, not IgE allergies.
• Read labels carefully and ask when eating out.
• Keep asthma well controlled.

Useful links

• NHS — Food allergy
• Allergy UK
• BSACI — Find an allergy clinic