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* Please see TIA's post on What Is It: Preservatives and Parabens and Are They Safe and Why Products Need Preservatives
Sodium Metabisulfite is an organic salt used as a disinfectant and preservative agent in cosmetics and personal care products, according to Wikipedia. It is also considered a reducing agent that donates hydrogen molecules to other substances in cosmetics and personal care products. This ingredient can sometimes function as an antioxidant, preventing or slowing deterioration of formulas caused by chemical reactions with oxygen. Sodium Metabisulfite is seen as an ingredient primarily in hair care products, such as formulas for permanent waves, hair bleaches, hair dyes, colors and tints, and also in some bath and skin care products (CosmeticsInfo.org).
Sodium Metabisulfite is FDA approved and has received its Generally Recognized as Safe (GRAS) rating. It is also CIR approved for use in cosmetics.
Safety Measures/Side Effects:
According to the Cosmetics Database, Sodium Metabisulfite is considered a moderate hazard ingredient, due to concerns regarding cancer, developmental and reproductive toxicity, immunotoxicity, irritation and organ system toxicity, with lesser concerns regarding neurotoxicity. The Association of Occupational and Environmental Clinics classifies it as a human immune and respiratory toxicant, and other organizations have classified it as an irritant and "as expected to be toxic or harmful."
However, according to a study published in the International Journal of Toxicology entitled "Final report on the safety assessment of sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, ammonium bisulfite, sodium metabisulfite and potassium metabisulfite," undiluted Sodium Metabisulfite was not found to be an irritant to rabbits following occlusive exposures, but at 50% was irritating to guinea pigs following repeated exposure. This is a concentration that would not be found in cosmetics, hair, or personal care products. It was also found to be negative in mutagenicity studies, and there is not a concern regarding penetration or contamination because "Skin penetration would be low due to the highly charged nature of these particles and any sulfite that did penetrate would be converted to sulfate by the enzyme sulfate oxidase." It was ultimately assessed that Sodium Metabisulfite is a safe ingredient in cosmetics and personal care products.
It is worth noting that the MSDS for Sodium Metabisulfite labels it as "Hazardous in case of skin contact (irritant), of ingestion, of inhalation. Slightly hazardous in case of skin contact (permeator), of eye contact (irritant)" and that it "may be toxic to upper respiratory tract, skin, eyes." However, this is in higher, undiluted concentrations than found in cosmetics and personal care products, and is rather related to occupational exposures.
Recommended Products w/ Sodium Metabisulfite:
Skin Effects Advanced Brightening Complex, Nutra-Lift Dark Spot Fade Gel, Preventin-AT Age Spot Treatment, Xen-Tan Deep Bronze Body Tanner and Face Tanner