What causes a hernia?

Nature/Nurture. Most hernias develop due to a "birth defect" of sorts, where natural holes in the abdominal wall present in fetal life fail to close. This may manifest itself at birth or require years of "exertion" before the hole reaches a size large enough to be evident. Other hernias are strictly "wear-and-tear" phenomena, although it is believed that they occur in-part due to inherently weak tissue.
See below. It is a defect or weakening in the abdominal wall (usually near the groin or in the lower abdomen). This can be caused by many things including past surgery, injury, excess weight, and others. Then a piece of intestine can penetrate the defect. The risk is strangulation and death of the intestine. This can happen anytime - that's why it should be treated.

Related Questions

What causes recurrent hernias that mesh does not stay in place. Are there any ithers ways to repair hernias instead of mesh?

Hernias and mesh. Generally the mesh is "tacked in place" by staples or a suture and should not wander. Are you sure its the mesh moving versus another hernia - around the mesh? I might try a different surgeon. Read more...
Recurrent hernias. The incidence of hernia recurrence is dependent on the size and type of hernia, patient factors such as obesity, and the method of repair. The use of mesh has significantly reduced the rate of recurrence, but it is not perfect. When a hernia does recur it is not due to the mesh moving as much as persistence of the same factors which caused the hernia, leading to a "blow-out" . Read more...

What causes groin hernias?

No specific cause. Groin or inguinal hernias are quite common in men, and may be somewhat hereditary. It is a weakness in the fibers that may be weak since birth. Can sometimes be associated with heavier lifting or repeated straining. Read more...
Unknown. The exact cause for any individual is unknown, but several factors are know to cause hernias such as a genetic collagen disorder, lifting heavy objects, coughing, or any activity that involves sudden and repeated increases in pressure inside the abdominal cavity. Read more...

What causes inguinal hernias?

Congenital/acquired . The path taken for testicular descend can stay open or predispose one to inguinal herniation - this is aka indirect hernia. The hernia more common with accident, sport injury or heavy lifting as with construction workers is frequently through the direct inguinal space - direct inguinal hernia. Read more...
Congenital/acquired . The path taken for testicular descend can stay open or predispose one to inguinal herniation - this is aka indirect hernia. The hernia more common with accident, sport injury or heavy lifting as with construction workers is frequently through the direct inguinal space - direct inguinal hernia. Read more...

What causes diaphragmatic hernia?

Lack of development. Poor or incomplete development of the pluroperitoneal membrane which forms the diaphragm muscle. Read more...

What causes a diaphragmatic hernia?

Birth defect. It is a failure of the tissue that will form the diaphragm musle to fuse in the midline and separate the abdominal compartment from the chest compartment. Read more...
Hole in diaphragm. Most commonly, a diaphragmatic hernia occurs as a congenital anomaly in a baby. A diaphragmatic hernia can also occur as a result of trauma, either penetrating with the diaphragm pierced, or blunt with the diaphragm popped/burst. In all cases, a diaphragmatic hernia requires surgery. Read more...