Allantoin is a product of adenine and guanine metabolism. Allantoin exists as two enantiomers (R)-(-)-allantoin and (S)-(+)-allantoin that are subject to enzimatic racemization. The spontaneous decomposition of upstream intermediates and the nonenzymatic racemization of allantoin lead to an accumulation of (R)-allantoin, because the enzymes converting allantoin into allantoate are specific for the (S) isomer. The enzyme allantoin racemase catalyzes the reversible conversion between the two allantoin enantiomers, thus ensuring the overall efficiency of the catabolic pathway and preventing allantoin accumulation. The naturally-occurring (+)-allantoin was isolated from leaves of Platanus orientah and from the urine of cattle. (-)-Allantoin was obtained by degradation of the dextrorotatory form of the racemate by allantoinase from soy bean meal or from the liver of Raja clavata.

Allantoin is a metabolic intermediate of a wide variety of organims: from bacteria to vegetals and animals. Allantoin is a skin active ingridient with keratolytic, moisturizing, anti-irritant properties, promotes renewal of epidermal cell and accelerates wounds healing. Allantoin possesses one chiral center thereby exists in the two enantiomeric forms R-(-) and S-( ). Enzymes that catalyze the formation of (S)-allantoin from the product of the urate oxidase reaction have been identified. The two proteins encoded by mouse genes catalyze two consecutive steps following urate oxidation to 5-hydroxyisourate (HIU): hydrolysis of HIU to give 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) and decarboxylation of OHCU to give S-( )-allantoin. Urate oxidation produces racemic allantoin on a time scale of hours, whereas the full enzymatic complement produces dextrorotatory allantoin on a time scale of seconds. Scioderm is developing Allantoin (Zorblisa; SD-101), as a novel topical therapy for patients with epidermolysis bullosa.