Urea is a physiological substance occurring in human tissues, blood, and urine. The amount in urine is of the order of 2%. The extraction of pure urea from urine was first accomplished by Proust in 1821, and it was first synthesized by Wöhler in 1828.1 Urea is also a major constituent of the water-soluble fraction of the stratum corneum, as a component of the natural moisturizing factor (NMF).2 The level of urea in the stratum corenum is significantly reduced in patients with atopic dermatitis.3