E221 (Sodium sulfite) is a chemical compound, disodium salt of sulphurous acid.  It belongs to the sulphite group.

The sulphite group includes:

What it is used for and where

Food

It is labeled as E221 in the list of food additives with preservative function.

It improves the ability to knead the bread and used in eggs (1), beer, caramel, baked goods and salads.

Also used in wine.

Although it is used as a generic preservative, it is not allowed in meat products.

Acceptable daily dose: 0.7 mg / kg body weight

It can give allergic reactions (2).

Cosmetics

It is a restricted ingredient as a Relevant Item III/99 and V/9 in the Annexes of the European Cosmetics Regulation 1223/2009: "The SCCNFP is of the opinion that inorganic sulfites and bisulfites do not pose a health risk when used in cosmetic products at concentrations up to 0.67% in oxidative hair dye products, up to 6.7 % in hair waving/straightening products, up to 0.45 % in self-tanning products for the face and up to 0.40 % in self-tanning products for the body (all expressed as SO2)" (3). 

Antioxidant agent. Ingredient that counteracts oxidative stress and prevents cell damage. Free radicals, pathological inflammatory processes, reactive nitrogen species and reactive oxygen species are responsible for the ageing process and many diseases caused by oxidation.

Waving and straightening agent for hair. It is an ingredient that enables straightening and/or waving by permanently changing the shape or configuration of the keratinous hair fibres.

Preservative. Any product containing organic, inorganic compounds, water, needs to be preserved from microbial contamination. Preservatives act against the development of harmful microorganisms and against oxidation of the product.

Reducing agent. Ingredient that facilitates permanent hair waving by adjusting the pH to an optimal level.

Safety

Symptoms related to sulphite sensitivity can be of varying nature and importance. The most common are headache and generalised itching or swelling, but cases of nausea, bronchoconstriction, diarrhoea, hypotension and shock have also occurred (4).

EFSA's Scientific Panel on Food Additives and Flavourings assessed the risk for toxic elements in sulphur dioxide (E 220-228), based on data submitted by stakeholders, and concluded that the EU specification maximum limits for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced (5).

Sodium sulfite studies

Molecular Formula: Na₂O₃S   Na₂SO₃

Molecular Weight: 126.037 g/mol

UNII: VTK01UQK3G

CAS: 7757-83-7  68135-69-3

EC Number: 231-821-4

PubChem Substance ID 329824427

MDL number MFCD00003503

Synonyms:

• Sodium sulfite
• Disodium sulfite
• Sodium sulfite anhydrous
• Sulfurous acid, disodium salt
• Sulftech
• Natrium sulfurosum
• sodiumsulfite
• Natriumsulfid
• Natriumsulfit
• Natrii sulphis
• Anhydrous sodium sulfite
• E221
• CHEMBL1945334
• CHEBI:86477

References______________________________________________________________________

(1) Effects of sulfhydryl compounds, carbohydrates, organic acids, and sodium sulfite on the formation of lysinoalanine in preserved egg.
Luo XY, Tu YG, Zhao Y, Li JK, Wang JJ. - J Food Sci. 2014 Aug;79(8):T1621-8. doi: 10.1111/1750-3841.12543. 

(2) Contact allergy to sodium sulfite and its relationship to sodium metabisulfite.
Oliphant T, Mitra A, Wilkinson M.  -  Contact Dermatitis. 2012 Mar;66(3):128-30. doi: 10.1111/j.1600-0536.2011.02029.x.

(3)  0648/03 - Opinion concerning Inorganic Sulfites and Bisulfites

(4) Gunnison AF, Jacobsen DW. Sulfite hypersensitivity. A critical review. CRC Crit Rev Toxicol. 1987;17(3):185-214. doi: 10.3109/10408448709071208.

Abstract. Sulfiting agents (sulfur dioxide and the sodium and potassium salts of bisulfite, sulfite, and metabisulfite) are widely used as preservatives in foods, beverages, and pharmaceuticals. Within the past 5 years, there have been numerous reports of adverse reactions to sulfiting agents. This review presents a comprehensive compilation and discussion of reports describing reactions to ingested, inhaled, and parenterally administered sulfite. Sulfite hypersensitivity is usually, but not exclusively, found within the chronic asthmatic population. Although there is some disagreement on its prevalence, a number of studies have indicated that 5 to 10% of all chronic asthmatics are sulfite hypersensitive. This review also describes respiratory sulfur dioxide sensitivity which essentially all asthmatics experience. Possible mechanisms of sulfite hypersensitivity and sulfur dioxide sensitivity are discussed in detail. Sulfite metabolism and the role of sulfite oxidase in the detoxification of exogenous sulfite are reviewed in relationship to the etiology of sulfite hypersensitivity.

(5) EFSA Panel on Food Additives and Flavourings (FAF); Younes M, Aquilina G, Castle L, Engel KH, Fowler PJ, Frutos Fernandez MJ, Fürst P, Gundert-Remy U, Gürtler R, Husøy T, Manco M, Mennes W, Moldeus P, Passamonti S, Shah R, Waalkens-Berendsen I, Boon P, Cheyns K, Crebelli R, FitzGerald R, Lambré C, Mirat M, Ulbrich B, Vleminckx C, Mech A, Rincon AM, Tard A, Horvath Z, Wright M. Follow-up of the re-evaluation of sulfur dioxide (E 220), sodium sulfite (E 221), sodium bisulfite (E 222), sodium metabisulfite (E 223), potassium metabisulfite (E 224), calcium sulfite (E 226), calcium bisulfite (E 227) and potassium bisulfite (E 228). EFSA J. 2022 Nov 24;20(11):e07594. doi: 10.2903/j.efsa.2022.7594. 

Abstract. Sulfur dioxide-sulfites (E 220-228) were re-evaluated in 2016, resulting in the setting of a temporary ADI of 0.7 mg SO2 equivalents/kg bw per day. Following a European Commission call for data, the present follow-up opinion assesses data provided by interested business operators (IBOs) and additional evidence identified in the publicly available literature. No new biological or toxicological data addressing the data gaps described in the re-evaluation were submitted by IBOs. Taking into account data identified from the literature search, the Panel concluded that there was no substantial reduction in the uncertainties previously identified in the re-evaluation. Therefore, the Panel considered that the available toxicity database was inadequate to derive an ADI and withdrew the current temporary group acceptable daily intake (ADI). A margin of exposure (MOE) approach was considered appropriate to assess the risk for these food additives. A lower confidence limit of the benchmark dose of 38 mg SO2 equivalents/kg bw per day, which is lower than the previous reference point of 70 mg SO2 equivalents/kg bw per day, was estimated based on prolonged visual evoked potential latency. An assessment factor of 80 was applied for the assessment of the MoE. At the estimated dietary exposures, when using a refined exposure scenario (Data set D), MOEs at the maximum of 95th percentile ranges were below 80 for all population groups except for adolescents. The dietary exposures estimated using the maximum permitted levels would result in MOEs below 80 in all population groups at the maximum of the ranges of the mean, and for most of the population groups at both minimum and maximum of the ranges at the 95th percentile. The Panel concluded that this raises a safety concern for both dietary exposure scenarios. The Panel also performed a risk assessment for toxic elements present in sulfur dioxide-sulfites (E 220-228), based on data submitted by IBOs, and concluded that the maximum limits in the EU specifications for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced.