Potassium Metabisulfite

Potassium metabisulfite is an inorganic salt that functions as a reducing agent in cosmetic formulations. It works by breaking down chemical bonds, which makes it particularly useful in hair-waving and hair-straightening treatments. Beyond hair care, it also serves as a preservative and antioxidant in some skincare products, helping to prevent oxidation and extend shelf life.The ingredient is metabolised in the body to sulfate, a naturally occurring compound. It is widely used in professional and consumer hair care products, though it appears in a smaller proportion of general skincare form…

Potassium metabisulfite functions as a reducing agent by donating electrons to break disulfide bonds. In hair care, these bonds hold the hair's structure in place; breaking them temporarily allows the hair to be reshaped. Once the hair is set in its new form and the product is rinsed away, new bonds reform, holding the new shape.As a preservative, it prevents the growth of microorganisms that could compromise product safety and stability. Its antioxidant properties work by preventing unwanted chemical reactions that occur when ingredients are exposed to oxygen or light.

Potassium metabisulfite is typically used in professional hair treatments and specialised formulations rather than daily skincare products. If you are using a hair-straightening or hair-waving product containing this ingredient, follow the product instructions carefully and rinse thoroughly after the recommended contact time. As with any chemical treatment, a patch test on a small area before full application is sensible practice.

Generally well-tolerated at cosmetic concentrations. Individuals with known sensitivity to sulfites should exercise caution, though topical reactions are rare; those with severe sulfite sensitivity should consult a healthcare professional before use.