A hernia develops when the outer layers of the abdominal wall weaken, bulge, or actually rip. The hole in this outer layer allows the inner lining of the cavity to protrude and to form a sac.

Any part of the abdominal wall can develop a hernia. However, the most common site is the groin. A hernia in the groin area is called an inguinal hernia (inguinal is another word for groin). Inguinal hernias account for 80 percent of all hernias. In an inguinal hernia, the sac protrudes into the groin towards and sometimes into the scrotum. Although most common in men, groin hernias can also occur in women.

Another type of hernia develops through the navel, and it is called an umbilical hernia.

A hernia that pushes through past a surgical incision or operation site is called an incisional hernia.

Femoral hernias are similar to inguinal hernias. The femoral hernia occurs when abdominal contents are forced through the "femoral canal". Typically this type of hernia forms near the crease of leg in the abdominal region, but in an area relatively lower than the more common inguinal hernia. The two types of hernias are often too difficult to tell apart in diagnosis, which is why a hernia specialist is often required to confirm diagnosis. Femoral hernias are more likely to become incarcerated or strangulated because of their location, which is why repair is strongly advised upon diagnosis of this type of hernia.

Epigastric hernias occur between the lower part of the breastbone and the naval and is caused by a weakness or opening in the fibrous tissue of the abdomen. This type of hernia usually consists of fatty tissue and rarely contains intestinal tissue. Although generally small in size (no bigger than a golf ball), epigastric hernias can easily become pinched in their small area, sometimes causing a great deal of pain.