A thickened tooth whitening composition in gel form comprises hydrogen peroxide or a hydrogen peroxide precursor, and a thickening polymer or copolymer comprising a pendant sulfonic acid group moiety, preferably hydroxyethyl acrylate/sodium acryloyldimethyltaurate copolymer. Gels in accordance with the invention exhibit an extended shelf life without requiring refrigeration or other special storage conditions. A particularly efficacious manner of method of whitening teeth comprises applying a volume of a gel in accordance with the invention onto the bristles of a toothbrush, applying a volume of a toothpaste onto the toothbrush bristles, and brushing one or more teeth to be whitened with the toothbrush bristles onto which the toothpaste and the thickened tooth whitening composition were applied for a sufficient period to cause the composition and toothpaste to mix together.
