Belly buttons smell when they are infected. The warm, moist crevice offered by a belly button is an inviting place for bacteria and fungi to grow. A smell and a discharge almost always mean an infection. Washing the belly button and keeping it dry can prevent infections.
Sometimes antibacterial or antifungal creams need to be applied to treat infections. Uncontrolled diabetes is a predisposing factor for developing belly button infections.
A medical condition called patent urachus can also cause a foul smell to emanate from the belly button. In patent urachus, the tube connecting the bladder and the umbilical cord in babies does not close off after birth. This open connection can lead to odor, infections and discharge from the belly button. Surgery is required to correct patent urachus.