Urea

What is urea?

Urea is an emollient that is widely used to moisturise and protect the skin (R). It is part of the natural moisturising factor of the skin (R), and can be found naturally in small quantities in the stratum corneum (R, R).

Is urea stable?

Urea tends to be unstable and to degrade into ammomium cyanate. This leads to an odour and an increase in pH that can make it difficult to use in cosmetic formulations (R). Its stability is known to be affected by its concentration, the pH of the formulation, and the temperature under which it is kept. Specifically, it is more stable at a pH of between 4 to 8, at lower temperatures and when its initial concentration is higher (R). Other ways to stabilise urea include using a lactate buffer (R), and adding a small amount of a lactone to the formulation (R).

Does urea get absorbed?

Urea permeates the skin well, possibly because of its small molecular size of only 60 Daltons (R, R). It has also been demonstrated to enhance the penetration of other compounds across the skin, including tretinoin (R), progesterone (R), corticosteroids (R, R) and cortisol (R).