Sodium metabisulfite is one of a group of preservatives known as sulphites. It is a food preservative, cosmetic and industrial bleaching agent, and an ingredient in the developing solution for film and photography. Evidence exists that it is also an immune-system toxin. As part of the group of sulphites, sodium metabisulfite can provoke reactions in people, particularly asthmatics, ranging from gastrointestinal discomfort and hives to asthma attacks.
Sodium metabisulfite is used as a preservative in foods such as baked goods, jams, wines, dried fruit and many sauces. Sulphites can be added before or after cooking. Fruits and raw vegetables used to be sprayed with sulphites, but this practice was banned by the U.S. Food and Drug Administration in 1986. Sodium metabisulfite is also used as an antibacterial agent in wine, although some manufacturers have begun using potassium metabisulfite instead. Some winemakers have claimed that sodium metabisulfite increases the sodium content of wine.
Sodium metabisulfite exists in both food-grade and non-food-grade forms. The non-food-grade form is an industrial bleaching and reducing agent; it is also used to remove excess chlorine from drinking water and as a photographic developing and fixing bath agent.
Sodium metabisulfite is an antioxidant additive in injectable medicines and is also used as a reducing agent in pharmaceuticals. Some medical lotions may contain sodium metabisulfite; even in topical preparations, however, sodium metabisulfite may induce allergic or sensitive reactions.
Asthma and Sulfites
Reactions to sodium metabisulfite are more common among asthmatics than in the general population and can be mild or severe. According to the World Health Organization's International Programme on Chemical Safety, 25 per cent of severe reactions to sulphites involved breathing difficulties, although reactions affected not only respiratory function but skin and gastrointestinal function as well. Hives, swelling and vomiting are all possible reactions.
Ingesting foods containing sodium metabisulfite can set off reactions if you are sensitive to sulphites. Regulations require manufacturers to list sulphites on ingredient labels. The Cosmetics Database notes that sodium metabisulfite, used in products such as moisturisers, sunscreens, cleansers and hair bleaches, may be toxic to the human immune system and may be a carcinogen.