Allantoin. Polarised light micrograph of allantoin (C4.H6.N4.O3) crystals. Allantoin is the metabolic end product of uric acid oxidation in all vertebrates except the higher apes and humans. However, it is present in the amniotic fluid and foetal urine. Allantoin promotes rapid cell regeneration and is used as an ingredient in wound and burn healing creams. It also has a skin- softening (keratolytic) effect and is used in many types of cosmetics.