The American Contact Dermatitis Society bestows the annual ‘honour’ of ‘Allergen of the Year‘ on an element, chemical, or group of chemicals in order “to draw attention to the agents causing the most significant clinical effects” — and sulfites / sulphites have received the dubious distinction for 2024.
Distinct from sulfates / sulphates, sulphites are perhaps more commonly known as preservatives and anti-oxidants in food, and are named as one of the top 14 declarable food allergens or food allergen groups in the UK and EU — the only chemical additive among the others, all 13 of which are foods — but they are not a recognised ‘top’ allergen in the US.
They are found in dried fruits, alcoholic beverages, fruit juices, pickled products and more, and will be seen emphasised (typically in bold) in lists of food ingredients, often towards the end of the list. Sulphur dioxide is E220 and the various sulphites fall in the range E221 (sodium sulphite) to E228 (potassium hydrogen sulphite).
But until now, awareness of sulphites’ potential as skin contact allergens in addition to dietary allergens has been under-recognised, and they are not always used on the various standard patch testing panels dermatologists use to diagnose skin allergies caused by contact dermatitis.
They are commonly found in cosmetics, particularly in hair dye and colouring products (see my article ‘Sulphite Free Hair Dye‘ for more), hair styling products, make-up and tanning products — for example to prevent colour oxidation, but also as general preservatives, including in other toiletries, and some medications.
The mechanisms behind the dermatological and the oral exposures and reactions to sulphites are different — so while dermatological reactions to exposures in cosmetics may result in rashes, redness and itching, often on the hands and face, food reactions may involve more typical allergy-like symptoms such as wheezing. That said, food exposures may also cause symptoms of dermatitis on the lips and mouth.
If, despite undergoing food / skin allergy testing, you have persisting symptoms, and you know you are exposing yourself to any of the sulphites — which can appear as ‘bisulphite‘ or ‘metabisulphite‘ as well as ‘sulphite’ on cosmetic products, typically preceded by a mineral such as sodium, calcium or potassium — then it may well be worth checking with your allergy consultants that these have been tested for and ruled out as possible triggers.