A hernia is a sac formed by the lining of the abdominal cavity (peritoneum). The sac comes through a hole or weak area in the strong layer of the belly wall that surrounds the muscle. This layer is called the fascia.Which type of hernia you have depends on where it is:Femoral hernia is a bulge in the upper thigh, just below the groin. This type is more common in women than men.Hiatal hernia occurs in the upper part of the stomach. Part of the upper stomach pushes into the chest.Incisional hernia can occur through a scar if you have had abdominal surgery in the past.Umbilical hernia is a bulge around the belly button. It occurs when the muscle around the belly button does not close completely after birth.Inguinal hernia is a bulge in the groin. It is more common in men. It may go all the way down into the scrotum.