The evidence on safety published to date tends to suggest that bleaching is a relatively safe procedure. Hydrogen peroxide breaks down into water and oxygen. Urea breaks down into carbon dioxide and ammonia. Normal body processes easily handle all four products. It has been suggested that peroxides are mutagenic and can boost the effects of known carcinogens. The American Dental Association (ADA), however, has found no evidence that, when used as directed, tooth whiteners increase cancer risk or cause other problems. The ADA has also acknowledged that some members of the public abuse bleaching products.