Many factors may cause a hernia.
What causes a hernia depends on the type of hernia. Hernias appear as a bulge beneath the skin. They occur most often in the abdomen, likely when the intestines protrude through a weakened abdominal wall. However, hernias can occur in other parts of the body. Johns Hopkins Medicine identifies seven types of hernias:
• Inguinal hernias, the most common type, occur when intestines protrude through the inguinal canal, which is located in the lower abdomen near the groin.
• Femoral hernias occur mostly in obese women when intestines protrude through a femoral artery passage located in the upper thigh.
• Epigastric hernias occur when intestines protrude through a portion of abdominal muscle between the breastbone and the navel.
• Umbilical hernias, common in newborns, occur next to the navel when part of the intestine protrudes through the abdominal wall.
• Parumbilical hernias are similar to umbilical hernias but occur after birth, most commonly in middle-aged women.
• Incisional hernias occur after surgery at the sight of an incision.
• Hiatal hernias occur when the stomach passes through an opening in the diaphragm into the chest.
The Cleveland Clinic reports an estimated five million Americans develop hernias each year. Only about 14 percent get a hernia surgically repaired, even though it can be a relatively simple outpatient procedure.
Hernias can be caused by increased pressure on the abdominal wall, a pre-existing abdominal wall weakness or a combination of both. A pre-existing weakness can occur at birth when the lining of the abdomen (peritoneum) does not close properly. Abdominal wall weakness, which occurs later in life, can be caused by age-related muscle deterioration, weakness from an operation, an injury or from pressure on the abdomen. This pressure can come from fluid build-up in the abdomen, coughing, pregnancy, excess weight or physical activity such as heavy lifting or straining during urination and bowel movements.
According to the Mayo Clinic, men are more prone to inguinal hernias due to the way the testicles form and relocate. The testicles form in the abdomen and then pass through the inguinal canal to the scrotum. The inguinal then closes, preventing the testicles from sliding back up into the abdomen. When the inguinal canal does not properly close, the result is a weakened abdominal wall.
Umbilical hernias, which occur when a section of intestines pass through weakened abdominal muscles, can occur in adults, but are most common in infants. They can occur at birth or later during infancy. Fetuses have a small opening in their abdominal muscles which allow the umbilical cord to pass through. This opening usually heals before birth. However, if it does not completely heal, a weakened area in the abdominal muscles can allow protrusion of intestines. According to Mayo Clinic, approximately 90 percent of umbilical hernias close in the first 12 months. with 10 percent taking a bit longer. Surgery is likely for umbilical hernias that don't correct by age 4.
In adults, umbilical hernias are caused by a combination of abdominal muscle weakness and other factors such as obesity, fluid in the abdomen, strenuous physical activity, coughing or multiple pregnancies.
Incisional hernias occur after surgery from a weakened abdominal wall tissue, in combination with another factor or factors. Scar tissue, which forms after surgery, can be thin or stretch, causing weakness in the abdominal wall. This weakness can lead to an incisional hernia if pressure is increased at the site of the incision from weight gain, pregnancy, vomiting, coughing or strain from a bowel movement.
A hiatal hernia occurs in the chest cavity and does not involve the intestines. In a hiatal hernia, the stomach passes through an opening in the diaphragm into the chest. This happens when tissue weakens around the hiatus, an opening that allows the esophagus to connect with the stomach. The top of the stomach then passes through the weak area into the chest cavity.
It's not known what causes hiatal hernias, but injuries to the area can be a preceding factor. In other cases, the person is born with a large hiatus or with weak tissue around the hiatus. As with other types of hernias, pressure from vomiting, sneezing, pregnancy, abdominal fluid or strenuous physical activity can cause a hernia to occur.