Sodium sulphite
A sulphite preservative that stops spoilage and discolouration in dried fruit, wine and other foods. Declared as a major allergen on UK labels.
Can trigger asthma attacks and breathing difficulties in sulphite-sensitive people, estimated at 5 to 13 percent of asthmatics. EFSA withdrew the acceptable daily intake in 2022 after finding evidence of nervous system effects and because industry declined to supply the new safety data regulators requested. High consumers across most age groups, including children, may exceed the exposure threshold EFSA set as acceptable.
What is it?
Sodium sulphite is the sodium salt of sulphurous acid, a white to yellowish powder that releases sulphur dioxide on contact with acids or heat. It belongs to the sulphite group of additives (E220 to E228), all of which are evaluated together as a class.
What does it do?
It acts as a preservative and antioxidant by releasing sulphur dioxide, which inhibits the enzymes that cause browning and kills spoilage bacteria, yeasts and moulds. It also prevents oxidation that degrades colour and flavour. In bread and baked goods it can condition gluten. It is not permitted in meat products in the UK and EU because it can mask the colour and smell changes that signal bacterial spoilage.
Where you will see it
Most commonly in dried fruits such as apricots, raisins and sultanas; wine and beer; fruit juices and cordials; shellfish and prawns (to prevent blackspot); potato products including instant mash; vinegar and pickles; starch and gelatine. On the label it may appear as 'sodium sulphite', 'E221', 'sulphur dioxide', or under the group term 'sulphites'. UK law requires the words 'contains sulphites' or 'contains sulphur dioxide' when the level in the ready-to-eat food is above 10mg/kg or 10mg/litre.
What the science says
Asthma and breathing reactions
Sulphites release sulphur dioxide gas when they meet stomach acid, and that gas can irritate and narrow the airways. Between 5 and 13 percent of people with asthma are estimated to be sulphite-sensitive, with the highest rates in those with severe or steroid-dependent asthma. Reactions can include wheezing, chest tightness and shortness of breath within minutes of eating sulphite-containing food. Rare anaphylactic reactions have also been reported.
Between 5 and 13 percent of people with asthma react to sulphites, with higher rates in those with steroid-dependent asthma.
Sulphites release sulphur dioxide on contact with gastric acid; the gas disperses back into the airways and triggers bronchoconstriction via a cholinergic reflex and, in some, IgE-mediated immune responses.
Sulphites are listed as one of the 14 major allergens under UK food law (Food Information Regulations 2014, assimilating EU Regulation 1169/2011), with mandatory label declaration above 10mg/kg or 10mg/litre.
EFSA withdrew the acceptable daily intake after finding nervous system signals
In 2016, EFSA set a temporary group acceptable daily intake of 0.7mg sulphur dioxide equivalent per kilogram of body weight per day for all sulphite additives, and found that high consumers in several age groups already exceeded it. By 2022, EFSA withdrew even that temporary ADI after industry declined to run the new toxicological studies regulators asked for. In its place EFSA used a margin of exposure approach and found the safety margin fell below the acceptable threshold for most population groups including children and adults, based on evidence of delayed nerve-signal responses in animal studies.
EFSA set a temporary group ADI of 0.7mg SO2 equivalents per kg body weight per day for E220-E228 in 2016, and found dietary exposure estimates exceeded this for all population groups studied.
In 2022 EFSA withdrew the temporary ADI because the toxicity database remained inadequate and industry submitted no new biological or toxicological data to close the identified gaps.
Using a margin of exposure approach based on a benchmark dose of 38mg SO2 equivalents per kg body weight per day (derived from prolonged visual evoked potential latency, an early sign of nervous system dysfunction), margins of exposure were below the acceptable level of 80 for most population groups except adolescents.
In 2025 the European Commission requested EFSA to model alternative lower maximum permitted levels to reduce dietary exposure, reflecting ongoing regulatory concern.
Effect on gut bacteria at food-relevant concentrations
A laboratory study found that sodium sulphite and sodium bisulphite inhibited or killed four species of beneficial gut bacteria at concentrations that fall within ranges found in sulphite-preserved food. The study does not prove the same happens in the human gut at typical food intake, but researchers noted that current safety standards were set without accounting for effects on the microbiome.
Sodium sulphite inhibited or killed four Lactobacillus and Streptococcus species at concentrations of 250 to 500 ppm in laboratory culture, levels the authors noted fall within the range regarded as acceptable by regulators.
Destroys thiamine (vitamin B1) in food
Sulphite ions cleave the thiamine molecule by reacting at the methylene bridge that holds its two ring structures together, degrading vitamin B1 content in sulphite-treated foods. This is one reason UK and EU regulations prohibit sulphites in meat and other foods that are important thiamine sources.
Sulphite ions cleave the thiamine molecule by a multi-step reaction, replacing the thiazole ring and rendering the vitamin inactive. The rate increases under acidic conditions.
Where it stands with the regulators
Who should be careful
People with asthma should be aware that sulphites can trigger attacks, particularly if asthma is severe or steroid-dependent. Anyone who has experienced breathing difficulties, hives or gastrointestinal reactions after wine, dried fruit or prawns should seek an allergy assessment. On UK labels, look for 'sulphites', 'sulphur dioxide', 'E221', or 'contains sulphites' in the ingredients or allergen box. The declaration is mandatory above 10mg/kg or 10mg per litre but some sulphite-containing foods may carry the additive at lower levels without declaration.
The honest read
The sulphite group is among the more regulatory-contested preservatives in EU food law. The 2016 EFSA review already found high consumers exceeding the ADI, and the 2022 follow-up withdrew even the temporary ADI after industry did not produce the new studies requested, leaving regulators without a firm safety number. The nervous system signals from animal studies are not yet confirmed in humans at typical food intake, and the regulator explicitly used a margin-of-exposure approach rather than drawing a firm causal line. The asthma link is better established, documented in clinical studies and recognised in UK allergen law. The gut bacteria finding is from controlled laboratory conditions and may not translate directly to what happens in the digestive tract. What is clear: the science here is not settled, the regulatory basis for current permitted levels is under active review, and the European Commission was actively modelling reductions in 2025.
Related additives
Common questions
Is E221 banned in the UK?
No. E221 is an authorised food additive in the UK and EU, listed on the FSA approved-additives register with effect from 31 December 2020. However, it is not permitted in meat products, where it would mask signs of bacterial spoilage. The safety assessment is under active regulatory review.
Why did EFSA withdraw the acceptable daily intake for sulphites?
In 2022 EFSA concluded that the available toxicity database was insufficient to set a reliable ADI. Industry operators were asked after the 2016 review to commission new toxicological studies to fill specific data gaps; they declined to do so. EFSA withdrew the temporary ADI it had set in 2016 and switched to a margin-of-exposure approach, which found safety margins were below acceptable thresholds for most population groups.
What foods contain E221?
Dried apricots and other dried fruit are among the highest-sulphite foods. It is also used in wine, beer, fruit juices, prawns and shellfish, instant mashed potato, vinegar, pickled foods and some gelatine products. On the label it may appear as E221, sodium sulphite, sulphur dioxide, or under the group statement 'contains sulphites'.
Is E221 vegan?
Yes. Sodium sulphite is a synthetic mineral-derived compound with no animal origin. It is suitable for vegan, vegetarian, halal and kosher diets.
Sources
- UK FSA: Sodium sulphite (E221) regulatory authorisation record
- UK FSA: Approved additives and E numbers
- EFSA: Scientific Opinion on re-evaluation of sulfur dioxide (E220) and sulphites (E221-E228), EFSA Journal 2016;14(4):4438
- EFSA: Follow-up re-evaluation of sulfur dioxide and sulphites (E220-E228), EFSA Journal 2022;20(11):7594
- EFSA: PMC full text of 2022 sulfites follow-up (PMC9685353)
- EFSA Supporting Publications 2025 EN-9754: Update of dietary exposure to sulfur dioxide and sulphites with alternative maximum levels
- Allergy UK: Sulphites and Airway Symptoms factsheet
- Anaphylaxis UK: Sulphite Allergy fact sheet
- UK FSA: Food allergen labelling and information requirements technical guidance
- Irwin & Fisher, Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food, PLOS ONE 2017
- Dwivedi & Arnold, A mechanism for sulphite ion reacting with vitamin B1 and its analogues, Food Chemistry 1984
- PMC article: Characterisation of bronchoconstrictor responses to sodium metabisulphite aerosol in atopic subjects (PMC1020876)
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