odd question but here is my answer from a slightly medical point. There is urea in the urine. urea is composed of nitrogen and carbon dioxide. This makes it very acidic. The purpose of urea is to open the pores so the medication that is added with it can "get in". Below is a pasted part from wickipedia describing the use of urea for skin.
"Urea is used in topical dermatological products to promote rehydration of the skin. If covered by an occlusive dressing, 40% urea preparations may also be used for nonsurgical debridement of nails."
This indicates that if you are using urea then it is added along with a moisturinzure. Alone it will dry out your skin or cause it to debride which means aiding in removing it.