Is ointment containing urea, used by women to remove stretch marks on the abdomen during pregnancy, considered impure?

Urea is a substance excreted with urine and is impure (najis), so creams mixed with it are not permissible to use unless it transforms through manufacturing into something else, whereby it becomes pure. As for industrial urea, it is not impure (najis), and creams mixed with it are not forbidden.