The hernia pouch or sac is the lining of the inside of the tummy wall. It pushes through the weakness at the tummy button. The sac has a fatty covering and inside there may be bowel or fatty tissue called omentum. The sac steadily gets larger and can be painful. The bowel and omentum may get stuck in the sac. Their blood supply can be cut off and the bowel and omentum can strangulate and die. This causes vomiting, great pain and is very serious. Umbilical hernias are very common and easily treated, particularly when small. If treated when they are small, this will prevent strangulation and make the strongest repair.