A synonym for carbamide: the excretory product of nitrogen metabolism produced in mammalian livers following the breakdown of amino acids. In foods, urea matters in several contexts. Its formation during wine fermentation is a cause for concern, since urea is a precursor of ethyl carbamate (urethane), a probable human carcinogen formed by reaction with ethanol during storage. As a fertilizer and ruminant feed supplement, urea use can lead to its presence in milk. Food-grade urea is also permitted as a fermentation aid and dough conditioner in some jurisdictions, but its indirect role in ethyl carbamate formation keeps it under toxicological watch.