Azodicarbonamide (ADC) has long been used by commercial bakers to strengthen dough, but it has been undertested. A 1999 review by various United Nations agencies concluded that "there are insufficient data on carcinogenic, reproductive, or developmental effects to assess the risk to human health of these endpoints.

Much of the concern about azodicarbonamide has to do with two questionable chemicals that form when bread is baked. The first chemical, semicarbazide (SEM), caused lung and blood vessel cancer in mice. It did not cause cancer in mice. In 1976, the International Agency for Research on Cancer considered SEM a carcinogen in mice, but concluded in 1987 that animal data were "limited" and that SEM was "unclassifiable" for human carcinogenicity.

The second breakdown product, polyurethane, is a recognized carcinogen. Urethane levels in bread pose a small risk to humans if the ADC is used at the maximum allowable level (45 ppm in bread). Baking bread increases urethane levels. However, when used at a concentration of 20 ppm (probably the amount used by some commercial bakeries), a 1997 FDA study found "only a slight increase" in polyurethane. (Some forms of polyurethane in bread are not made with azodicarbonamide.)

Considering that many breads do not contain azodicarbonamide, and that its use slightly increases exposure to carcinogens, this is hardly a chemical we need in our food supply. The Delaney Amendment prohibits the use of additives that cause cancer in humans or animals, which appears to require the FDA to ban their use. At the very least, the FDA should reduce the amount allowed.
First draft by R. Cary, S. Dobson, and E. Ball
Published under the joint sponsorship of the United Nations Environment Programme, the International Labor Organization and the World Health Organization and produced within the framework of the Inter-Organization Program for the Sound Management of Chemicals
French (‎pp. 21-22)‎ and Spanish Executive Summary