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.