Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), SO2−
3. The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used.
Sulfites are substances that naturally occur in some foods and the human body. They are also used as regulated food additives.
The structure of the sulfite anion can be described with three equivalent resonance structures. In each resonance structure, the sulfur atom is double-bonded to one oxygen atom with a formal charge of zero (neutral), and sulfur is singly bonded to the other two oxygen atoms, which each carry a formal charge of −1, together accounting for the −2 charge on the anion. There is also a non-bonded lone pair on the sulfur, so the structure predicted by VSEPR theory is trigonal pyramidal, as in ammonia (NH3). In the hybrid resonance structure, the S-O bonds are equivalently of bond order one and one-third.
- Sulfur dioxide, which is not a sulfite, but a closely related chemical oxide
- Potassium bisulfite or potassium metabisulfite
- Sodium bisulfite, sodium metabisulfite or sodium sulfite
Sulfites occur naturally in all wines to some extent. Sulfites are commonly introduced to arrest fermentation at a desired time, and may also be added to wine as preservatives to prevent spoilage and oxidation at several stages of the winemaking. Sulfur dioxide (SO2) protects wine from not only oxidation, but also from bacteria. Without sulfites, grape juice would quickly turn to vinegar.
Organic wines are not necessarily sulfite-free, but generally have lower amounts and regulations stipulate lower maximum sulfite contents for these wines. In general, white wines contain more sulfites than red wines and sweeter wines contain more sulfites than drier ones.
In the United States, wines bottled after mid-1987 must have a label stating that they contain sulfites if they contain more than 10 parts per million.
In the European Union an equivalent regulation came into force in November 2005. In 2012, a new regulation for organic wines came into force. In the United Kingdom, similar laws apply. Bottles of wine that contain over 10 mg/l sulfites are required to bear "contains sulphites" on the label. This does not differ whether sulfites are naturally occurring or added in the winemaking process.
Most beers no longer contain sulfites, although some alcoholic ciders contain them. Although shrimp are sometimes treated with sulfites on fishing vessels, the chemical may not appear on the label. In 1986, the Food and Drug Administration in the United States banned the addition of sulfites to all fresh fruit and vegetables that are eaten raw.
Sulfites are counted among the top nine food allergens, but a reaction to sulfite is not a true allergy. Some people have positive skin allergy tests to sulfites indicating true (IgE-mediated) allergy. Chronic skin conditions in the hands, perineum, and face have been reported in individuals that regularly use cosmetics or medications containing sulfites. Occupational exposure to sulfites have been reported to cause persistent skin symptoms.
It may cause breathing difficulty within minutes after eating a food containing it. Asthmatics and possibly people with salicylate sensitivity (or aspirin sensitivity) are at an elevated risk for reaction to sulfites. Anaphylaxis and life-threatening reactions are rare. Other potential symptoms include sneezing, swelling of the throat, hives, and migraine.
A 2017 study has shown negative impacts of sulfites on bacteria found in the human microbiome.
Use and labeling regulations
In 1986, the U.S. Food and Drug Administration banned the use of sulfites as preservatives on foods intended to be eaten fresh (such as salad ingredients). This has contributed to the increased use of erythorbic acid and its salts as preservatives.
In the U.S., labeling regulations do not require products to indicate the presence of sulfites in foods unless it is added specifically as a preservative; however, many companies voluntarily label sulfite-containing foods. Sulfites used in food processing, but not specifically added as a preservative, are only required to be listed if there are more than 10 parts per million (ppm) in the finished product.
The products most likely to contain sulfites (fruits and alcoholic beverages less than 10ppm) do not require ingredients labels, so the presence of sulfites usually is undisclosed.
In Australia and New Zealand, sulfites must be declared in the statement of ingredients when present in packaged foods in concentrations of 10 mg/kg (ppm) or more as an ingredient; or as an ingredient of a compound ingredient; or as a food additive or component of a food additive; or as a processing aid or component of a processing aid. In the United Kingdom sulfites are included in the list of known allergens and should the concentration of sulfites exceed 10 ppm, bottles of wine should bear the warning 'contains sulphites' 
The sulfites that can be added to foods in Canada are potassium bisulfite, potassium metabisulfite, sodium bisulfite, sodium dithionite, sodium metabisulfite, sodium sulfite, sulfur dioxide and sulfurous acid. These can also be declared using the common names sulfites, sulfates, sulfiting agents.
High sulfite content in the blood and urine of babies can be caused by molybdenum cofactor deficiency disease which leads to neurological damage and early death unless treated. Treatment, requiring daily injections, became available in 2009.
3 bisulfite ion
5 metabisulfite ion
- Sulfurous acid
5 persulfate ion
4 sulfate ion
2 hyposulfite ion
3 thiosulfate ion
- SO2 sulfur dioxide
- SO3 sulfur trioxide (a sulfate precursor)
- Category:Sulfites for a list of sulfites.
- Grant v The Australian Knitting Mills
- Housecroft CE, Sharpe AG (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.
- "Sulphites: One of the ten priority food allergens". Health Canada. Archived from the original on 7 July 2016. Retrieved 6 April 2015.
- "Allergies: Sulfite Sensitivity". WebMD. 1 February 2007. Retrieved 2007-09-10.
- Zacharkiw B (July 15, 2008). "Can't hold the sulphites". Montreal Gazette.
- Spencer B. "Sulfur in Wine Demystified".
- McCarthy E, Ewing-Mulligan M (2012). Wine for dummies (5th ed.). Hoboken, N.J.: Wiley. ISBN 978-1-118-28872-6.
- Breton F. "Many organic wines contain sulfites". French Scout.
- "Food Labeling - Community Legislation". European Commission. Retrieved 2007-09-10.
- "Commission Implementing Regulation (EU) No 203/2012". Official Journal of the European Union. 8 March 2012.
- Safonov D. "7 Myths of Natural Wines with no sulphites added". Organic Wine Club.
- Fortin ND (2009). Food Regulation: Law, Science, Policy and Practice. John Wiley and Sons. p. 288. ISBN 0-470-12709-0.
- Randhawa S, Bahna SL (2009). "Hypersensitivity reactions to food additives". Current Opinion in Allergy and Clinical Immunology. 9 (3): 278–83. doi:10.1097/ACI.0b013e32832b2632. PMID 19390435.
- "Sulphites - One of the nine most common food products causing severe adverse reactions". Canadian Food Inspection Agency.
- "Sulfite Allergy". The Australasian Society of Clinical Immunology and Allergy (ASCIA).
- Vally H, Misso NL (2012). "Adverse reactions to the sulphite additives". Gastroenterology and Hepatology From Bed to Bench. 5 (1): 16–23. PMC . PMID 24834193.
- "Sulfites" (PDF). California Department of Public Health: Food and Drug Branch.
- "Sulfite Sensitivity". Cleveland Clinic.
- Govias GD. "Sulfite Sensitivity". American Academy of Allergy Asthma and Immunology.
- "Sulfites". American Academy of Allergy Asthma and Immunology.
- "Preservative: Sulfur Dioxide and Sulfites". World Health Organization.
- Arora H, Kaur R (April 2008). "The role of diet in migraine headaches" (PDF). Delhi Psychiatry Journal. Delhi Psychiatry Society. 11 (1): 69–72. Retrieved 21 March 2016.
- "What you need to know about sulphites". Eat Right Ontario. Retrieved 6 April 2015.
- Irwin SV, Fisher P, Graham E, Malek A, Robidoux A (2017-10-18). "Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food". PLOS One. 12 (10): e0186629. doi:10.1371/journal.pone.0186629. PMC . PMID 29045472.
- Hui YH (2006). Handbook of Food Science, Technology and Engineering. CRC Press. pp. 83–32. ISBN 0-8493-9848-7.
- "Foods That Contain Sulfites". Sulfite Allergies. 2012-3-7. Retrieved 2015-10-21.
- "For asthma sufferers:the facts about sulphites in food". Food Standards Australia New Zealand (FSANZ).
- "Sulphite Free Diet: sulphites, sulfites and sulphur dioxide in food". Organic Wine Club.
- Tedmanson S (November 5, 2009). "Doctors risk untried drug to stop babys brain dissolving". The Times. London. Retrieved May 13, 2010.