A hiatus hernia happens when part of the stomach pushes up through the opening in the diaphragm where the esophagus passes through. This opening, called the hiatus, normally fits snugly around the esophagus. When the muscles and tissues around it weaken or stretch, the stomach can slide upward into the chest cavity. The condition affects 15 to 20 percent of people in Western populations, and while it often causes no symptoms at all, understanding what causes it helps explain why some people develop problems like acid reflux.
How the Diaphragm Normally Keeps the Stomach in Place
Your diaphragm is a dome-shaped muscle that separates your chest from your abdomen. The esophagus passes through a small gap in this muscle, the hiatus, before connecting to the stomach just below. A flexible band of tissue called the phrenoesophageal ligament anchors the junction between the esophagus and stomach in place. This ligament is designed to resist the stomach being pulled upward into the chest while still allowing enough movement for normal swallowing and changes in body position.
When a hiatus hernia develops, there are typically three structural problems at work. The tissue lining the abdominal cavity stretches and forms a loose sac that extends up through the hiatus. The ligament anchoring the esophagus to the diaphragm weakens. And the muscular ring of the hiatus itself widens beyond its normal size, creating enough room for the stomach to push through.
Pressure From Below Is the Main Driver
The single biggest mechanical cause of a hiatus hernia is sustained or repeated pressure inside the abdomen pushing upward against the diaphragm. Think of it like squeezing a tube of toothpaste: when pressure builds below the diaphragm, the stomach gets forced toward the path of least resistance, which is the hiatus.
Several common activities and conditions create this kind of pressure:
- Chronic coughing or sneezing, which repeatedly spikes abdominal pressure
- Straining during bowel movements, especially from long-term constipation
- Frequent vomiting, which forces the stomach contents and the stomach itself upward
- Heavy lifting or intense exercise, particularly movements that involve bearing down
- Pregnancy and childbirth, where the growing uterus pushes upward on the diaphragm for months at a time
- Chronic obesity (a BMI over 30), which creates constant excess pressure in the abdomen
Any one of these alone may not be enough. But when they combine, or persist over years, the cumulative strain on the hiatus gradually loosens its grip on the esophagus.
Why Age Is the Strongest Risk Factor
Hiatus hernias become dramatically more common with age. The tissues that hold the hiatus together, including muscle fibers, connective tissue, and the phrenoesophageal ligament, naturally lose elasticity and strength over decades. This is the same process that weakens joints, skin, and other connective tissues throughout the body. By the time someone reaches their 60s or 70s, the muscular collar around the hiatus may have loosened enough that even modest increases in abdominal pressure can push the stomach through.
This age-related weakening explains why many hiatus hernias are discovered incidentally during imaging for something else, in people who never had symptoms. The hernia formed so gradually they never noticed.
Being Born With a Larger Hiatus
Some people are simply born with a wider-than-normal hiatal opening, which makes herniation more likely later in life. This isn’t the same as a congenital diaphragmatic hernia, a serious birth defect where the diaphragm fails to form completely, allowing abdominal organs to crowd the chest cavity during fetal development. Congenital diaphragmatic hernia is a separate, much rarer condition. In 10 to 15 percent of those cases, it occurs as part of a syndrome affecting multiple body systems, sometimes caused by changes in single genes or chromosomal abnormalities.
For most adults with a hiatus hernia, the genetic contribution is subtler. If your parents had one, you may have inherited a naturally wider hiatus or weaker connective tissue that predisposes you to the same problem. Researchers are still working to identify the specific genes involved in diaphragm development that might play a role.
Two Types With Different Causes
Not all hiatus hernias are the same, and the type matters because it affects both the cause and the potential consequences.
Sliding Hernias (Type I)
Over 95 percent of hiatus hernias are the sliding type. In this version, the junction where the esophagus meets the stomach slides upward through the hiatus intermittently. It may move up when you lie down or strain, then slip back into position when you stand. Sliding hernias are the ones most closely linked to gradual pressure and age-related weakening. They’re also the type most associated with acid reflux, because the displacement disrupts the natural valve mechanism that keeps stomach acid from flowing backward.
Paraesophageal Hernias (Types II Through IV)
The remaining 5 to 10 percent are paraesophageal hernias, sometimes called rolling hernias. In a Type II hernia, the upper part of the stomach bulges up through the hiatus beside the esophagus, while the esophagus-stomach junction stays in its normal position below the diaphragm. Type III is a combination where both the junction and part of the stomach herniate. Type IV is the most severe: other organs besides the stomach, such as the colon or spleen, can push through the hiatus into the chest.
Paraesophageal hernias are more likely to result from a significant structural defect in the hiatus rather than just gradual loosening. They can also develop after upper abdominal surgery that disrupts the anatomy around the hiatus.
Obesity Deserves Special Attention
Carrying excess abdominal weight is one of the most modifiable causes of hiatus hernia. Unlike a single episode of heavy lifting, obesity creates constant, around-the-clock pressure on the diaphragm. Fat deposits around the abdomen press inward and upward, pushing the stomach toward the hiatus with every breath. This is why weight loss is one of the first recommendations for people with a hiatus hernia causing reflux symptoms. Reducing that baseline pressure can shrink a sliding hernia or at least reduce how often and how far it slides.
Injury and Surgery
Physical trauma to the chest or abdomen can damage the diaphragm directly, tearing or weakening the hiatal opening. Car accidents, falls, and penetrating injuries are the most common culprits. Surgery in the upper abdomen or lower chest can also disrupt the structures around the hiatus, either by directly disturbing the diaphragm or by creating scar tissue that changes how forces are distributed across the muscle. These cases are less common than the gradual, pressure-related variety, but they tend to cause larger hernias because the structural damage is more sudden and significant.
What Ties It All Together
In most cases, a hiatus hernia doesn’t develop from a single cause. It results from a combination of factors working together over time. Someone born with a slightly wider hiatus who develops a chronic cough in their 50s and carries extra weight around their midsection has three overlapping forces all weakening the same structure. The hiatus was designed to hold, but it has limits. When the tissue gets stretched past those limits often enough, the stomach finds its way through.