Urea is the primary nitrogenous product of protein metabolism in mammals and some fish species. The substance was first synthesized in 1828 and has proved valuable for various pharmaceutical, industrial and agricultural uses.

View a second image of urea crystallites.

Sometimes urea is not processed properly within the body, often a sign of a urea cycle disorder. The condition is genetically inherited and is caused by a deficiency of one of the enzymes that is supposed to remove the waste product nitrogen, generated by protein metabolism, from the blood. The nitrogen accumulates in people with urea cycle disorders and is stored as ammonia, rather than being transferred into urea and exiting the body with the urine. Extremely toxic, the substance migrates through the blood into the brain where it can cause severe damage and even death.

Commercially, urea is produced by the dehydration of ammonium carbamate at elevated temperature and pressure levels. The ammonium carbamate is attained by the direct reaction of liquid ammonia with liquid carbon dioxide. Typically, both reactions are generated simultaneously in a high-pressure reactor. The urea is then sold for use in fertilizers, barbiturates, resins, lubricants, and aviation fuel.