Sulfur dioxide or sulphur dioxide (‘sulfites’) is the chemical compound with the formula SO₂. It is a toxic gas responsible for the smell of burnt matches. It is released naturally by volcanic activity and is produced as a by-product of copper extraction and the burning of fossil fuels contaminated with sulfur compounds. Sulfur dioxide is added to most wines, the exception being wine with no added sulfites.

Research into reducing sulfites: See Julie-Ann Hansjosten.

Other names: Dioxyde de soufre (French).