Sodium sulfite is a chemical compound, disodium salt of sulphurous acid.

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.

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