Hernias happen when tissue or an organ pushes through a weak spot in the muscle or connective tissue that normally holds it in place. This almost always requires two things working together: a structural weakness in the body wall and enough internal pressure to force tissue through that weakness. About 14.6 million people worldwide had an inguinal, femoral, or abdominal hernia in 2021, with men affected at roughly 2.5 times the rate of women.
The Two-Part Mechanism Behind Every Hernia
Think of a hernia as a slow-motion blowout in a tire. First there needs to be a thin or damaged spot in the wall, and then enough pressure from the inside to push something through it. Researchers describe this as a staged process: a small plug of connective tissue gets wedged into a potential opening by coughing, straining, or any spike in abdominal pressure. That plug gradually stretches the lining of the abdominal cavity inward, creating a pocket. Over time, the pocket grows large enough for intestine, fat, or other tissue to slip into it.
This is why a single moment of heavy lifting rarely causes a hernia out of nowhere. In most cases, the weak spot already existed, and the strain was simply the final push.
Why Some People Have Weak Spots to Begin With
The abdominal wall isn’t uniformly strong. Certain areas, like the groin, the navel, and the diaphragm, have natural openings where blood vessels, cords, or the esophagus pass through. These built-in gaps make those locations vulnerable. But weakness also runs deeper than anatomy.
Collagen, the protein that gives connective tissue its strength, plays a central role. People who develop hernias tend to produce less collagen overall and have a skewed ratio of collagen types. One study found 17.3% less total collagen and 23.7% less of the strongest collagen type in the abdominal wall tissue of hernia patients compared to people without hernias. Even on the non-herniated side of their bodies, patients with direct inguinal hernias showed tissue that stretched more easily than normal, suggesting a body-wide predisposition rather than a localized problem.
Animal research reinforces this idea. When scientists induced a collagen-crosslinking deficiency in rats that also had a small anatomical defect, hernias developed reliably. Either problem alone wasn’t enough. The combination was what mattered.
Congenital Causes in Infants and Children
In babies, inguinal hernias are almost always caused by a developmental structure called the processus vaginalis, a small tunnel that forms during fetal development to allow the testicles to descend into the scrotum (or to accompany a ligament in girls). This tunnel normally closes before or shortly after birth. When it stays open, abdominal contents can slide into it, creating a hernia. This is why infant hernias are treated with a simple surgical closure of the tunnel rather than a full repair of the muscle wall.
Interestingly, research suggests that even many adult inguinal hernias trace back to this same congenital opening. The rate of open tunnels found during abdominal surgery doesn’t increase with age, which argues against these hernias being purely “wear and tear” injuries. Many adults likely carry a small, silent opening from birth that only becomes a clinical hernia when pressure or tissue weakening tips the balance.
Groin Hernias: Direct vs. Indirect
The groin is the most common hernia location, and there are two distinct types depending on exactly where the tissue pushes through. Indirect inguinal hernias travel through the inguinal canal, the same passageway the testicles use during fetal development. These are linked to that persistent opening from birth and are the most common type in younger men.
Direct inguinal hernias push through a different spot, a region of the lower abdominal wall where the muscle and connective tissue are naturally thinner. These are more closely tied to age-related tissue degradation and collagen loss, and they become more common in middle-aged and older adults.
Hiatal Hernias and the Diaphragm
Not all hernias involve the abdominal wall. A hiatal hernia occurs when part of the stomach pushes upward through the opening in the diaphragm where the esophagus passes through. The causes are somewhat different from groin hernias. Age-related weakening of the diaphragm muscle is the most common factor, which is why hiatal hernias are most frequent in people over 50. Obesity also increases risk by adding constant upward pressure against the diaphragm.
Other triggers include trauma to the area, being born with an unusually large opening in the diaphragm, or repeated intense pressure from chronic coughing, vomiting, or straining during bowel movements. Heavy exercise and lifting can contribute as well.
Incisional Hernias After Surgery
Any abdominal surgery that involves cutting through the muscle wall creates a potential weak point. An incisional hernia develops when tissue pushes through a previous surgical site that hasn’t healed with full strength. The main causes are inadequate closure during the original surgery and postoperative wound infections that compromise healing. Factors that impair tissue repair, like poor nutrition, obesity, diabetes, or smoking, also raise the risk significantly.
Pressure Triggers That Push Tissue Through
Once a weak spot exists, anything that raises pressure inside the abdomen can be the triggering event. The most common culprits include:
- Chronic coughing from smoking, asthma, or lung disease
- Straining during bowel movements due to chronic constipation
- Heavy lifting at work or during exercise
- Sneezing during allergy season or illness
- Obesity, which creates sustained abdominal pressure
As a Cleveland Clinic surgeon has noted, if you’re predisposed to a hernia, a coughing fit or a bout of constipation is just as likely to trigger it as lifting something heavy. The pressure source matters less than the underlying vulnerability.
How Pregnancy Changes the Abdominal Wall
Pregnancy creates a unique combination of hernia risk factors. The growing uterus progressively increases intra-abdominal pressure while simultaneously stretching the abdominal muscles. The rectus abdominis muscles lengthen, separate, and change their angle of attachment as pregnancy advances.
On top of the mechanical stress, the hormone relaxin, which the body produces to loosen pelvic ligaments for delivery, also breaks down collagen throughout the body. Relaxin stimulates enzymes that degrade the connective tissue matrix, reducing the structural integrity of the abdominal wall. This hormonal effect may explain why some women develop umbilical hernias during pregnancy or shortly after, and why hernias that are repaired before or during pregnancy sometimes recur.
How Age and Muscle Loss Raise Risk
People aged 65 to 69 consistently show the highest hernia rates across every world region. The reasons go beyond simple wear and tear. Sarcopenia, the age-related loss of skeletal muscle mass and strength, affects roughly 10% of adults over 65. As the abdominal wall muscles thin and weaken, they provide less resistance against internal pressure.
This muscle loss isn’t limited to aging alone. Serious illness, cancer, prolonged inactivity, and poor nutrition can all accelerate muscle wasting at any age. The result is the same: a weakened abdominal wall that is less capable of containing the organs behind it. This is one reason hernias are more common in people with chronic diseases, not just in those who are older.
The Gender Gap
Men develop hernias at dramatically higher rates than women. In 2021, the global prevalence was roughly 295 per 100,000 in males compared to 114 per 100,000 in females, and this gap widens with age. The primary reason is anatomical: the inguinal canal in men is larger because it accommodates the spermatic cord, and the processus vaginalis has further to travel during fetal development, creating more opportunity for it to remain open. Women have a smaller inguinal canal with less structural vulnerability, though they are more prone to femoral hernias, which occur just below the groin crease.