Hydrates at low percentages and dissolves thickened skin at high ones.
Urea is unusual in that its behaviour changes with concentration. Below about 10% it acts as a humectant, drawing in water. Above that it becomes keratolytic, breaking down the protein bonds in thickened or scaly skin — which is why 10–20% formulas are the standard recommendation for keratosis pilaris and rough heels.
skinfrndly is educational and is not medical advice. Recommendations are generated from the answers you gave and general dermatological guidance — they cannot account for your full history. For persistent or severe skin conditions, or before starting anything new during pregnancy, speak to a doctor or dermatologist.