Urea contains other ingredients such as catechols when it comes in liquid form from the human body
. See Haist for further information.
Urea, NH2-CO-NH2, is a development accelerator because it swells gelatin and improves diffusion, but it has a counter effect. The swelled gelatin is a longer diffusion path, and the gelatin is softer.
So, too much can cause reticulation and slower development.
You must be careful with these types of accelerants.
Good luck to you.
PE