Acetic acid /əˈsiːtɨk/, systematically named ethanoic acid /ˌɛθəˈnoʊɨk/, is an organic compound with the chemical formula CH3COOH (also written as CH3CO2H or C2H4O2). It is a colourless liquid that when undiluted is also called glacial acetic acid. Vinegar is roughly 3–9% acetic acid by volume, making acetic acid the main component of vinegar apart from water. Acetic acid has a distinctive sour taste and pungent smell. Besides its production as household vinegar, it is mainly produced as a precursor to polyvinylacetate and cellulose acetate. Although it is classified as a weak acid, concentrated acetic acid is corrosive and can attack the skin.