Allantoin is an imidazolidine-2,4-dione that is 5-aminohydantoin in which a carbamoyl group is attached to the exocyclic nitrogen. It has a role as a vulnerary, a human metabolite, a Saccharomyces cerevisiae metabolite and an Escherichia coli metabolite. It is a member of ureas and an imidazolidine-2,4-dione.