What Is a Hernia? Types, Causes, and Mesh Repair

A hernia occurs when an organ or tissue pushes through a weak spot in the muscle or connective tissue that normally holds it in place. The most familiar type, inguinal hernia, accounts for the vast majority of cases and appears as a bulge in the groin, but hernias also develop in the abdomen, the diaphragm, at old surgical incision sites, and even around internal structures where there is no visible bulge at all. The condition is extraordinarily common, and the science behind why it happens, who should get surgery, and which repair works best has shifted meaningfully in recent years.

Why Weak Spots Exist in the First Place

Humans are unusually prone to hernias compared with other mammals, and the reason is structural. In four-legged animals the inguinal canal, the passage through the abdominal wall where blood vessels and reproductive structures travel, points upward relative to the ground. Gravity pulls abdominal contents away from it. When humans began walking upright, that same canal shifted to face downward, placing it directly in the path of gravitational force from the organs above.¹ Every cough, heavy lift, or sustained strain pushes abdominal pressure straight toward this anatomical weak point.

Beyond anatomy, some people’s connective tissue is inherently weaker. Research on patients with recurrent inguinal hernias has found that their tissues produce a shifted ratio of collagen types. The body makes two main structural collagens: type I, which provides tensile strength, and type III, which is thinner and more pliable. In hernia patients, the ratio of type I to type III is significantly lower, driven by overproduction of the weaker type III collagen.² This imbalance appears not just at the hernia site but also in distant skin samples from hernia patients, suggesting the issue is systemic rather than local.³ This helps explain why hernias run in families and why some people develop them repeatedly despite repair.

Connective tissue disorders amplify the problem. Patients with Ehlers-Danlos syndrome, a group of inherited conditions that affect collagen structure, develop not only inguinal hernias but also hiatal hernias, diaphragm weakness, and rectal prolapse at elevated rates.⁴

Common Types and Who Gets Them

Inguinal hernias are by far the most common, making up roughly three-quarters of all abdominal wall hernias. They occur overwhelmingly in men, because the inguinal canal in males is wider to accommodate the spermatic cord. But women develop inguinal hernias too, and they are disproportionately affected by femoral hernias, which occur just below the inguinal canal where the femoral vessels pass into the thigh. Femoral hernias carry higher risk: studies show significantly higher incarceration and strangulation rates in women and in femoral hernia types specifically, along with worse outcomes when treatment is delayed.⁵

Umbilical hernias appear at or near the belly button and are common in newborns, where most close on their own by age four or five. In adults, they tend to develop in settings of increased abdominal pressure: obesity, pregnancy, or chronic heavy lifting. Diastasis of the rectus abdominis, a separation of the midline abdominal muscles that affects roughly a third to over two-thirds of postpartum women, often coexists with umbilical hernia.⁶

Internal hernias are rare and can be dangerous precisely because they produce no visible bulge. Bowel loops slip through an internal opening, such as a gap near the duodenum, and may become trapped. Diagnosis requires a high index of suspicion and skilled imaging, because delayed recognition can lead to bowel ischemia or infarction.⁷

Hiatal Hernias and Reflux

Not every hernia involves the abdominal wall. A hiatal hernia occurs when the upper stomach slides upward through the diaphragm’s esophageal opening into the chest cavity. It is one of the most common contributors to gastroesophageal reflux disease. The mechanism is well understood: the hernia weakens the lower esophageal sphincter by reducing its length and pressure, impairs the ability of the diaphragm’s muscle fibers to act as a backup valve, and creates a pocket of acid that can reflux back into the esophagus during swallowing.⁸

Large hiatal hernias that do not slide back into place on their own are particularly problematic because they also slow the normal clearing of acid from the esophagus, especially when lying down.⁹ Many people with small sliding hiatal hernias have no symptoms and need no treatment. When symptoms do arise, acid-suppressing medication is usually the first step, with surgical repair reserved for large or complicated cases.

When You Can Safely Wait

One of the more counterintuitive findings in hernia research is that not every inguinal hernia needs immediate surgery. For men whose hernia causes little or no pain, watchful waiting is a legitimate strategy. An individual-participant meta-analysis of long-term follow-up data from randomized trials confirmed that watchful waiting is safe and is not associated with increased mortality or complications compared with early repair.¹⁰

The catch is that most men eventually need the operation anyway. About a third of those who choose watchful waiting cross over to surgery within three years, and roughly two-thirds do so within ten years, most commonly because the hernia starts causing pain.¹¹ One randomized trial tracked patients for twelve years and found a cumulative crossover rate of about 64%, with incarceration, the feared complication where bowel gets trapped, occurring in only about 4% of the watchful waiting group.¹² So the acute risk of waiting is low, but the long game favors eventual repair for most people. The practical takeaway: if your hernia barely bothers you, there is no emergency. You and your surgeon can plan a repair on your schedule rather than rushing into one.

When incarceration does occur, certain warning signs suggest the trapped bowel may already be losing blood supply. Low sodium levels on a blood test, for instance, should prompt urgent surgical exploration in patients presenting with an incarcerated hernia.¹³

Mesh Repair and Why It Became Standard

For most of the twentieth century, hernia surgery meant stitching the edges of the defect together under tension. The Shouldice repair, perfected at a dedicated clinic in Ontario, was long considered the gold standard of tissue-based techniques. It works well in expert hands but has a meaningful recurrence rate. A meta-analysis of randomized trials comparing Shouldice to the Lichtenstein technique, which reinforces the repair with a flat piece of synthetic mesh, found a recurrence rate of about 4% for Shouldice versus under 1% for Lichtenstein.¹⁴ Longer-term follow-up from a separate randomized trial confirmed that tension-free mesh repair was superior, with almost all recurrences after mesh occurring within the first year.¹⁵

Mesh is not a single product. It comes in heavyweight and lightweight versions, and animal studies show that heavyweight mesh triggers more inflammation and foreign-body reaction than lightweight mesh, though both achieve similar tensile strength after implantation.¹⁶ The trend in hernia surgery has shifted toward lighter meshes and smaller pore sizes to reduce stiffness and chronic discomfort without sacrificing strength.

Laparoscopic and Robotic Approaches

Open Lichtenstein repair remains widely used, but laparoscopic techniques have been available for decades. The two main approaches are TAPP (transabdominal preperitoneal), which enters the abdomen and then places mesh behind the abdominal wall, and TEP (totally extraperitoneal), which avoids entering the abdominal cavity entirely. A network meta-analysis found the two are equivalent in operative time, complications, pain, return to work, and recurrence, though TAPP was associated with slightly longer hospital stays.¹⁷ In practice, the choice between them often comes down to surgeon training and preference.

Robotic hernia repair has grown rapidly, marketed on the promise of better ergonomics and three-dimensional visualization. The outcomes data so far, however, paint a more complicated picture. The RIVAL randomized trial found that robotic repair took almost twice as long as traditional laparoscopic repair and cost more than double, with no measurable ergonomic benefit for the surgeon.¹⁸ A meta-analysis confirmed longer operative times and substantially higher costs in the robotic group, with no differences in safety or postoperative outcomes compared with standard laparoscopy.¹⁹ A separate observational study reported higher reoperation and readmission rates in the robotic group, along with a greater proportion of serious complications.²⁰ The robot may eventually prove its value for complex abdominal wall reconstructions, but for routine inguinal hernia repair, the evidence does not yet justify the added expense.

Chronic Pain After Repair

Hernia surgery is one of the most performed operations in the world, which means even a modest complication rate affects a lot of people. Up to 16% of patients experience chronic pain after groin hernia repair.²¹ The pain can come from nerve entrapment in the mesh or scar tissue, mesh shrinkage pulling on surrounding structures, or unrelated causes that mimic hernia symptoms. Managing it starts with ruling out a recurrence and other diagnoses, and if conservative treatment fails, surgical options include removing the mesh and cutting the three nerves that supply sensation to the groin area. This is worth knowing before surgery, not as a reason to avoid repair but so you can discuss nerve-sparing techniques and mesh selection with your surgeon in advance.

Incisional Hernias and How Surgeons Try to Prevent Them

When someone has abdominal surgery through a midline incision, the closed wound can weaken over time and give way to a hernia. Incisional hernias are common after open abdominal operations, and they are frustrating because they represent a complication of a prior surgery rather than a primary disease. How the original incision was closed turns out to matter enormously. A randomized trial showed that closing the fascia with small, closely spaced bites of suture cut the incisional hernia rate roughly in half compared with the traditional large-bite technique, without increasing adverse events.²² A later meta-analysis pooling multiple studies confirmed these results: small-bite closure reduced the risk of hernia, surgical site infection, and wound separation.²³

European and American hernia society guidelines now recommend the small-bite continuous suturing technique with a slowly absorbable suture as the standard for midline closures. For patients at high risk of developing an incisional hernia, prophylactic mesh placement at the time of the original operation can also be considered.²⁴ A similar principle applies to patients receiving a permanent stoma: placing mesh around the stoma site at the time of its creation reduces the rate of parastomal hernia by more than half compared with no mesh, without increasing peristomal complications.²⁵

When incisional hernias do grow large, standard mesh repair may not suffice because the edges of the defect are too far apart to bring together. A technique called component separation allows the surgeon to release specific layers of the abdominal wall musculature so that the fascia can be advanced back to the midline, closing gaps as wide as 20 centimeters. The trade-off is a more extensive dissection that carries its own risks of wound complications and fluid accumulation.

The “Sports Hernia” That Usually Is Not a Hernia

Athletes who develop chronic groin pain are sometimes told they have a “sports hernia,” a term that has caused considerable confusion. In most cases, there is no actual hernia at all. The pain arises from tears or strains of the muscles and tendons that attach near the pubic bone, leading to instability of the pubic symphysis. On physical examination, no hernia bulge can be felt.²⁶ The preferred term in sports medicine is now “athletic pubalgia,” which more accurately describes the musculotendinous injury without implying a structural defect through the abdominal wall. Treatment may include rest, physical therapy, and in refractory cases, surgical repair of the torn tissue. Dynamic ultrasound can help distinguish true inguinal hernias from soft-tissue injuries in athletes with groin complaints.²⁷

Hernias in Children

Pediatric inguinal hernias have a different origin than adult ones. During fetal development, a finger-like pouch of peritoneum called the processus vaginalis extends through the inguinal canal, guiding testicular descent in boys and accompanying the round ligament in girls. Normally this pouch closes before or shortly after birth. When it remains open, it creates a ready-made channel for bowel or fluid to slip through, producing an indirect inguinal hernia or a communicating hydrocele.²⁸ Because the processus vaginalis can remain patent on the opposite side as well, there has been longstanding debate about whether to explore the other groin during surgery. Variations in the smooth muscle and cellular composition of the processus vaginalis wall may help determine which children are more susceptible to developing a contralateral hernia later.²⁹

The Global Access Gap

Hernia repair is sometimes called a bellwether operation for a health system’s surgical capacity, and a global cohort study of nearly 7,000 patients across income settings found stark disparities. Mesh was used in about 96% of repairs in high-income countries, about 78% in middle-income countries, and just 45% in low-income countries. Thirty-day complication rates followed a similar gradient: about 6% in high-income settings, 8% in middle-income ones, and nearly 17% in low-income countries. Reoperation rates ranged from about 1% to over 4%.³⁰ Perhaps most telling, incarcerated or strangulated hernias accounted for roughly 31% of presentations in low-income countries versus under 5% in high-income ones, reflecting delayed access to elective surgery that forces patients to present only when complications have already set in. Improving mesh availability and timely surgical access in resource-limited settings is one of the more straightforward ways to reduce a substantial burden of preventable morbidity.