In cases of hydronephrosis, it is not certain whether facial swelling will occur.

Since the human body has two kidneys, the kidneys have strong compensatory capabilities. Even if one kidney is completely damaged, if the other kidney remains healthy, the remaining kidney can still perform the function of two kidneys. It can ensure sufficient excretion of water and metabolic waste. When water is sufficiently excreted, swelling should not occur.

However, if both kidneys are affected by hydronephrosis, or if the opposite kidney also has problems, then the ability of the kidneys to excrete water may decrease. With both kidneys having issues, it can lead to poor and insufficient water excretion, consequently causing swelling, such as bilateral eyelids, facial areas, and both ankles.