Many centuries ago the Romans discovered that adding substances containing sulphites to foods makes them last longer and helps preserve their colour and flavour.
Sulphites work by releasing sulphur dioxide, a gas, which can cause the airway to become irritated and constricted. Less than 2% of the general population are believed to be allergic to sulphites, but in asthmatics it is much higher at between 5 and 13%.
An unpleasant reaction
Almost all of us are affected by food allergies or food intolerance at some stage of our lives. We’ve all had an unpleasant reaction to something we ate and wondered if we have an allergy. Fortunately true allergies are relatively rare, and only around four percent of the total population have a true allergic reaction to one or more foods.
Read: Allergic to food additives?
The most common food allergens are:
- Wheat (gluten) and other grains
- Nuts, especially peanuts
Allergy or sensitivity
Many people say they’re allergic to something when it’s actually only a sensitivity or intolerance. The difference between an allergy and a sensitivity/intolerance lies in the way the body responds to the substance. An allergy involves the immune system, whereas in the case of a sensitivity/intolerance the reaction is mainly triggered in the digestive system.
Read: Allergy tests that work
An allergic reaction happens when your immune system identifies a protein in food as an invader and launches an immune-mediated reaction. The most common type is an Immunoglobulin E (IgE)-mediated reaction followed by the release of chemicals like histamine from mast cells. In extreme cases an allergic reaction can result in anaphylaxis, which causes your blood pressure to drop and your airways to close – and can be deadly if not treated in time. (Anaphylaxis can be treated with an epinephrine injection, available in an auto-injector.)
Sulphur in foods
In the UK sulphites are recognised as a potential allergen, and have to be labelled on food or drink products if they appear at a certain concentration or above.
Read: The truth about food labels
Sulphites, including sulphur dioxide (SO2) are basically food preservatives used to prevent browning or discoloration of foods. In South Africa sulphur dioxide is commonly used to preserve dried fruit. Sulphites are also extensively used in wine, beer and other alcoholic beverages. Medicines and cosmetics may also contain sulphites.
Other foods that commonly contain sulphites are:
- Cookies, crackers, pizza base
- French fries and instant mashed potatoes
- Fruit juices
- Canned fruits and vegetables
- Pickles, olives and salad dressings
- Noodle, rice and soup mixes
Sulphites that are commonly added to foods are: sulphur dioxide, potassium bisulphate, potassium metabisulphate, sodium bisulphite, sodium dithionite, sodium metabisulphite, sodium sulphite and sulphurous acid.
Common reactions to sulphites
A 2009 study of the clinical effects of sulphite additives listed a range of reactions:
- Hypotension (low blood pressure)
- Abdominal pain
- Asthmatic reactions (Most studies report a 3–10% prevalence of sulphite sensitivity among asthmatic subjects following ingestion of these additives.)
The authors add that in addition to episodic and acute symptoms, sulphites may also contribute to chronic skin and respiratory symptoms. There are some theories, but it remains unclear what exactly the underlying causes of sulphate sensitivity are.
Read: Treating allergies
The best remedy is to be aware and steer clear of dietary sources of sulphites and according to the study “minor modifications to diet or behaviour lead to excellent clinical outcomes for sulphite-sensitive individuals”.
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Allergy UK: Sulphites and Airway Symptoms. https://www.allergyuk.org/sulphites-and-airway-symptoms/sulphites-and-airway-symptoms
Pubmed: Clinical effects of sulphite additives. http://www.ncbi.nlm.nih.gov/pubmed/19775253
Foods Matter: Sulphite Allergy. http://www.foodsmatter.com/allergy_intolerance/sulphites/articles/sulphites.html
Healthline:Food Allergy vs. Sensitivity: What’s the Difference? http://www.healthline.com/health/allergies/food-allergy-sensitivity-difference
Health Canada: Sulphites - One of the ten priority food allergens. http://www.hc-sc.gc.ca/fn-an/pubs/securit/2012-allergen_sulphites-sulfites/index-eng.php