Sulfites

Sulfites are a group of preservative compounds (including sulfur dioxide and related “sulfite” salts) added to foods to prevent discoloration and spoilage. For instance, dried fruit and some potato products may be treated with sulfites to keep their color. These additives are safe for most people, but they can provoke severe allergy-like reactions (especially asthma symptoms) in a small sensitive minority of consumers. Because of this risk, the FDA prohibits using sulfites on fresh produce intended to be served raw (since 1986) and requires labels to disclose sulfite preservatives in foods that contain detectable levels above ~10 ppm.

Aliases / Common Names: “Sulfiting agents”; Sulfur dioxide (SO₂, E220); Sodium bisulfite (sodium hydrogen sulfite, E222); Potassium metabisulfite (potassium pyrosulfite, E224); and other related sodium/potassium sulfites and metabisulfites. Regulatory Status & Exposure: In the U.S., sulfites are GRAS additives but face specific restrictions. The FDA has banned sulfites on certain fresh foods (notably on raw salad bar produce since 1986) and in meats that are significant vitamin B₁ sources (due to sulfites destroying thiamine). Otherwise, they are allowed as preservatives in processed foods, with a requirement that any product containing ≥10 ppm of sulfites declare it on the label. Canada, the EU, and other regions similarly mandate labeling above a threshold, as sulfites are recognized globally as a sensitizing substance. An international expert panel (JECFA) set a group Acceptable Daily Intake at 0–0.7 mg per kg body weight for sulfites (expressed as SO₂). The European Food Safety Authority initially affirmed this ADI, but after re-evaluating in 2016–2022, EFSA found data gaps and evidence that high consumers could exceed safe intake margins. EFSA withdrew the sulfites ADI in 2022 and switched to a conservative margin-of-exposure risk assessment. At extreme intake levels (for example, frequent large servings of sulfited foods), EFSA noted the safety margin may be insufficient – raising a potential concern – though typical dietary exposures for most people remain within tolerable bounds. Technical Evidence: The best-documented hazard of sulfites is acute respiratory hypersensitivity. Controlled clinical studies confirm that a subset of asthmatics (approximately 5% of those with severe asthma) will experience bronchoconstriction after ingesting sulfite-containing foods. These reactions can be serious: sulfite-sensitive individuals have suffered life-threatening asthma attacks, and past incidents include several deaths before protective measures were instituted. Mechanistically, sulfites can release sulfur dioxide gas upon contact with acids (such as in the stomach or in acidic beverages), which is believed to trigger reflex airway narrowing in susceptible persons. Unlike common food allergens, these reactions are usually not mediated by IgE antibodies – other pathways (including neural reflex and possibly a deficiency in sulfite-metabolizing enzymes) have been implicated. Outside of hypersensitivity cases, toxicological data on sulfites do not indicate severe chronic risks at typical doses. They have not been linked conclusively to cancer or genetic damage: for instance, the International Agency for Research on Cancer classifies sulfites as Group 3 (not classifiable as to carcinogenicity, indicating no persuasive evidence of cancer risk). High-dose animal studies have observed some effects – e.g. a slowing of nerve signal responses in the brain at very large doses – suggesting a potential neurotoxic effect threshold. There have also been isolated findings of testicular changes or gastrointestinal irritation in animals exposed to extreme levels of sulfites, but these findings are not well confirmed and occurred at exposures far above normal dietary intake. Additionally, sulfiting agents are known to destroy vitamin B₁ (thiamine) in foods; this is a quality concern (reducing nutritional value) rather than a direct toxicity, but it prompted rules like the US prohibition on adding sulfites to vitamin-rich foods (to avoid negating their nutrient content). Overall, decades of evaluation by regulators and scientists indicate that apart from rare allergic-type reactions, sulfites are not overtly harmful to the general population at the concentrations used in foods. Ongoing research continues to monitor whether very high consumption could pose subtler risks, but current evidence supports their safety for the vast majority of consumers. Fast-Food Context: In fast-food supply chains, sulfites are mainly encountered in pre-processed ingredients rather than added during restaurant cooking. For example, potato products destined for frying (such as frozen french fries or hash brown shreds) may be treated with sulfites by suppliers to prevent enzymatic browning before cooking. Similarly, certain pickled vegetables, relishes, or dried fruit pieces used as toppings can contain sulfite preservatives to maintain color and shelf-life. Sulfites might also appear in some bakery items or dough conditioners used by fast-food manufacturers (sulfites help condition dough and prevent oxidation in some frozen dough products). It’s important to note that fresh produce in restaurants will not have added sulfites – e.g. lettuce, tomatoes, or fresh fruit served in salads or drinks – because the FDA’s 1986 rule prohibits restaurants from using sulfites on raw fruits and veggies that will be consumed fresh. Thus, the major exposure to sulfites from fast food would come from processed components (like a dried potato or pickle ingredient) rather than from freshly prepared items. Consumers who are sulfite-sensitive should be cautious with items like condiments, dressings, or certain sides that might include sulfited ingredients, and can check ingredient information or ask restaurants when in doubt. Sensitive Populations / Notes: The primary sensitive group for sulfites are people with asthma. Approximately 4–5% of asthmatic individuals (roughly 1 in 20 asthmatics, or about 1 in 100 people overall) have some degree of sulfite sensitivity. In this subgroup, ingesting sulfites can provoke asthma symptoms or allergic-like reactions; in extreme cases, exposure has caused anaphylactic shock or severe respiratory distress. These individuals must avoid sulfite-containing foods and beverages entirely – which is why the mandatory labeling of sulfites (for foods above 10 ppm) is so crucial. Notably, sulfite reactions in people without asthma are very uncommon and usually mild if they occur at all. There is no evidence that sulfites cause any chronic illness, cancer, or toxicity in the general healthy population at dietary levels. Therefore, outside of the context of asthma or sulfite-allergy management, most consumers do not need to worry about the small amounts of sulfites encountered in occasional fast-food meals.

We assign the limited tier using published research, regulatory guidance, and PRūF’s additive taxonomy. Restaurant usage is derived from public ingredient disclosures and mapped to menu items where this additive appears.