Although hydrogen peroxide is the main bleaching ingredient in teeth whitening products, you should always check the percentage used. A high concentration of hydrogen peroxide (mostly over 33%) should be avoided as it may cause issues like inflammation and other infections. Some products may contain citric acid, which should also be avoided. Citric acid can erode tooth surfaces and cause sensitivity. Be careful of whitening products that contain sodium chlorite as it can be poisonous when ingested.