An umbilical hernia happens when division of the intestine protrudes during the umbilical opening in the abdominal muscles. Umbilical hernias are familiar and usually harmless. They are most ordinary in infants, but they can influence adults as well. In an infant, an umbilical hernia may be particularly evident when the infant cries, causing the baby’s bellybutton to protrude. This is a classic sign of an umbilical hernia.