A bleach is a chemical that removes colors or whitens, often via oxidation. Common chemical bleaches include household chlorine bleach, a solution of approximately 3–6% sodium hypochlorite (NaClO), and oxygen bleach, which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate, sodium percarbonate, sodium persulfate, tetrasodium pyrophosphate, or urea peroxide together with catalysts and activators, e.g., tetraacetylethylenediamine and/or sodium nonanoyloxybenzenesulfonate. To "bleach" something is to apply bleach, sometimes as a preliminary step in the process of dyeing. Bleaching powder is calcium hypochlorite.
Many bleaches have strong bactericidal properties, and are used for disinfecting and sterilizing. Most bleaches are hazardous if ingested or inhaled, and should be used with care.