Sulphur dioxide
A gas used since Roman times to stop wine and dried fruit spoiling. One of the 14 major allergens UK food law requires to be declared on labels.
Can trigger wheezing, chest tightness and asthma attacks in people with asthma. At high dietary intakes, EU regulators flagged a potential concern for all age groups and withdrew the established daily limit in 2022 because the toxicity data were too incomplete to set a new one.
What is it?
Sulphur dioxide (SO2) is a colourless gas produced by burning sulphur. In food, it is used directly as a gas or dissolved in water to form sulphurous acid; it is also released by related sulphite salts (E221-E228). It is one of the oldest food preservatives in continuous use.
What does it do?
It works on two fronts. As an antioxidant, it mops up oxygen and blocks the enzymes that cause cut fruit and veg to brown. As an antimicrobial, it inhibits yeasts, moulds and bacteria by disrupting their cell membranes and metabolic enzymes, preventing fermentation and spoilage.
Where you will see it
Highest levels are in light-coloured dried fruits, particularly dried apricots (the vivid orange colour is a sign of SO2 treatment; untreated apricots turn brown). Also present in wine and cider, grape juice, beer, pickled foods, sausages and burger meat with vegetable or cereal content, dehydrated potatoes, frozen raw potato products, and fresh or frozen prawns. On a UK label it appears as 'sulphur dioxide', 'sulphites', or E220 (and E221-E228 for related salts), always required to be declared in bold or highlighted when above 10mg per kg or per litre.
What the science says
Asthma and respiratory reactions
Sulphur dioxide is an airway irritant. When eaten, sulphites in food react with stomach acid and release SO2 gas, which can reach the airway and cause bronchoconstriction. Fewer than 2% of the general population are affected, but 5-13% of people with asthma react, with steroid-dependent asthmatics at highest risk. Symptoms range from mild wheezing to severe breathing difficulty, usually appearing within minutes to an hour of consumption.
Sulphite sensitivity triggers asthma symptoms (wheezing, chest tightness, cough) in an estimated 5-13% of people with asthma, compared with under 2% of the general population.
Symptoms of sulphite reactions include asthma, urticaria, angioedema, abdominal pain, nausea, diarrhoea, and in rare cases anaphylactic shock. Anaphylaxis from sulphites has been reported but is rare.
Sulphite sensitivity is more common in people with poorly controlled asthma and those with marked airway hyperresponsiveness. Sensitivity reactions to sulphites typically do not respond to antihistamines.
EFSA withdrew the safe daily limit in 2022
In 2016, EFSA set a temporary group acceptable daily intake (ADI) of 0.7mg SO2 equivalents per kg body weight per day, noting that even then, estimated dietary intakes in all population groups exceeded this level. In 2022, after industry failed to supply the additional toxicological data requested, EFSA concluded the database was too incomplete to set any ADI at all and withdrew it. Instead, EFSA used a margin of exposure (MOE) approach and found that at high dietary intakes, the safety margin fell below the protective threshold for most population groups, indicating a potential concern. The science here is not settled.
In 2016, EFSA set a temporary group ADI of 0.7mg SO2 equivalents/kg body weight per day but noted that dietary exposure estimates already exceeded this for all population groups.
In 2022, EFSA withdrew the temporary group ADI because the toxicity database was inadequate to derive one. Using a margin of exposure approach, EFSA found MOEs below the protective threshold of 80 for all population groups at high dietary intake percentiles, raising a safety concern.
Neurotoxicity signals in animal studies
The 2022 EFSA review identified neurotoxic effects as the most relevant new concern. Animal studies found that sulphite intake caused prolonged visual evoked potential latency (a measure of how fast nerve signals travel from the eye to the brain) and increased lipid peroxidation in brain tissue. EFSA used this finding to derive its benchmark reference point. These are animal studies, not human trials, so direct applicability to people is uncertain.
Sodium metabisulphite caused dose-dependent prolongation of visual evoked potential latency and increased lipid peroxidation in rat brain tissue, suggesting neurological effects at dietary sulphite levels.
EFSA identified prolonged visual evoked potential latency as the critical endpoint for the 2022 risk assessment, deriving a benchmark dose lower confidence limit of 38mg SO2 equivalents/kg body weight per day from this animal evidence.
Sulphur dioxide destroys vitamin B1 (thiamine)
Sulphur dioxide reacts with and destroys thiamine (vitamin B1) in food, converting it to a form the body cannot absorb. For this reason, UK and EU law prohibit its use in foods considered a source of thiamine, such as meat products intended as staple foods. The practical relevance for people eating varied diets with occasional dried fruit or wine is likely low, but it is a genuine nutritional trade-off.
Sulphur dioxide destroys thiamine in food by cleaving its molecular structure; the degree of destruction is dose-dependent, with levels around 400mg/kg capable of depleting thiamine by roughly 50%.
Thiamine deficiency in cats and dogs has been documented following diets primarily consisting of sulphite-preserved pet meat.
Where it stands with the regulators
Who should be careful
People with asthma, particularly those with poorly controlled or steroid-dependent asthma, are at highest risk of breathing reactions. Anyone who has had a previous sulphite reaction should avoid it. On UK labels, look for 'sulphites', 'sulphur dioxide', or any of E220 to E228 in the allergen information, highlighted in bold.
The honest read
Sulphur dioxide's story sits in two distinct places. For people with asthma, the risk from eating it is well-documented and real, and the allergen-labelling law exists for this reason. For everyone else, the picture is more complicated. EFSA estimated in both 2016 and 2022 that people who eat a lot of the foods where SO2 is most concentrated, particularly dried fruits, may be taking in more than would be considered comfortable under standard risk-assessment benchmarks. The difficulty is that EFSA could not complete a full toxicity assessment because industry did not supply the data it requested, so the regulator had to work with what it had, which it described as inadequate. The neurotoxicity signals that anchored the 2022 assessment come from animal studies, not human trials. What that means for people eating normal UK diets is genuinely unclear. The additive remains approved and in widespread use. The regulatory science here is unfinished.
Related additives
Common questions
Is E220 banned in the UK?
No. E220 is an approved food additive in the UK under assimilated EU Regulation 1333/2008, permitted in a range of foods including dried fruit, wine, sausages and pickled products. It is one of the 14 major allergens and must be declared on labels when present above 10mg per kg or litre.
Why did EFSA withdraw the acceptable daily intake for sulphur dioxide?
In 2016, EFSA set a temporary ADI noting the data were insufficient for a robust assessment. The European Commission asked industry to supply additional toxicological studies. When none were submitted, EFSA's 2022 follow-up concluded the database was still too incomplete to set any ADI and withdrew the existing temporary figure. EFSA instead applied a margin of exposure approach and identified a potential concern at high dietary intake levels for most population groups.
What foods contain E220?
The highest concentrations are typically found in light-coloured dried fruits, particularly dried apricots, where SO2 preserves the bright orange colour. It is also present in wine, beer and cider, fruit juices, sausages and burgers with vegetable or cereal content, pickled foods, mustard, dehydrated and frozen potato products, and fresh or frozen prawns.
Is E220 vegan?
Sulphur dioxide itself is produced by burning or oxidising sulphur and is not derived from animals. However, some of the products it is used in, particularly wine and cider, may be processed using animal-derived fining agents (such as casein, egg albumen or isinglass) that are separate from the SO2. The additive itself is vegan; the product it is in may not be.
Sources
- Approved additives and E numbers | Food Standards Agency
- EFSA Journal 2022: Follow-up of the re-evaluation of sulfur dioxide (E 220) and sulphites (E 221-228)
- EFSA Journal 2016: Scientific Opinion on the re-evaluation of sulfur dioxide (E 220) and sulphites as food additives
- PMC full text: EFSA 2022 follow-up re-evaluation of sulfur dioxide and sulphites
- Allergy UK: Sulphites and Airway Symptoms factsheet
- Anaphylaxis UK: Sulphites fact sheet
- Allergen guidance for food businesses | Food Standards Agency
- Erudus: Allergen Deep Dive - Sulphur Dioxide
- Food Navigator: Dietary intake of sulfites 'could be a safety concern': EFSA (2022)
- Ozturk et al., Dose-dependent effect of nutritional sulfite intake on visual evoked potentials and lipid peroxidation | PubMed
- BfR: Sulphur dioxide and sulphites: EFSA re-evaluation identifies health risks at high consumption
- EFSA Supporting Publications 2025: Update of dietary exposure to sulfur dioxide (E 220) and sulphites
- FSAI: Sulphur Dioxide and Sulphites
- Read & Harrington, Thiamine deficiency in cats and dogs associated with feeding meat preserved with sulphur dioxide | PubMed
Aaron Keen is the founder of NutraSafe. He researches and writes every additive entry himself, from the primary sources. About the research →
This is a guide, not medical advice. If an additive affects you, speak to your GP or a dietitian.
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