urea

[stereo]

Can some one tell me why this is good for the skin. I thought it was a waste product of urine.

[drtodorov]

Yes, it is a waste product. But it is not 'toxic waste'. In fact, ammonia, a toxic byproduct of protein metabolism, is converted in the body into urea, which is relatively nontoxic, so that it can be safely excreted without posoning the excretory system and other tissues.

Furthermore, urea is interesting chemically because it is a small polar molecule capable of disrupting hydrogen bonds (and possibly other weak polar bonds). When used topically, this has an effect of improving the penetration of active ingredients. Also, urea appears to have a moisturizing effect -- possibly also due to its ability to disrupt hydrogen bonds. Finally, urea has some antibmicrobial effect, so a cream with urea can often do with less preservatives (which are more toxic than urea itself).

All in all, there are many skin care ingredients that deserve far more to be labeled a 'waste' than urea.