A stomach hernia, most commonly called a hiatal hernia, happens when part of the stomach pushes upward through the diaphragm and into the chest cavity. The diaphragm is the large dome-shaped muscle separating your chest from your abdomen, and it has a small opening called the hiatus where your esophagus (swallowing tube) passes through to connect to the stomach. When the tissue around that opening weakens, the upper portion of the stomach can bulge through it. The causes range from aging and excess body weight to repeated physical strain, and often several factors combine.
How the Stomach Moves Out of Place
Your esophagus is anchored at the hiatus by a band of connective tissue called the phrenoesophageal ligament. This ligament keeps the junction between your esophagus and stomach positioned right at the diaphragm, where it belongs. When that ligament weakens or stretches, and the opening in the diaphragm widens, there’s nothing stopping the top of the stomach from sliding upward into the chest.
Once the stomach sits partially above the diaphragm, it tends to trap acid and digestive contents more easily, which is why heartburn and acid reflux are the most recognizable symptoms. The hernia itself isn’t always painful, and many people have one without knowing it.
The Two Main Types
Not all hiatal hernias look the same. The type depends on how the stomach moves through the opening.
- Sliding hiatal hernia (Type I): The most common type. The stomach and the junction where the esophagus meets the stomach both slide upward into the chest through the hiatus. The stomach may move up and down, especially when you swallow or strain.
- Paraesophageal hernia (Types II, III, IV): Less common but more concerning. The esophagus stays in its normal position, but a portion of the stomach squeezes up through the hiatus and sits next to the esophagus. In severe cases, a large section of the stomach can migrate into the chest. This type carries a risk of the stomach twisting or losing blood supply, which is a medical emergency.
A mixed type (Type III) combines features of both, where the junction slides up and additional stomach folds up alongside the esophagus.
Age and Tissue Weakening
Aging is one of the strongest contributors. Over time, the phrenoesophageal ligament undergoes degenerative changes: the collagen fibers that give it strength gradually break down, reducing its ability to snap back into position. The ligament loses tensile strength and elastic recoil, making it progressively less capable of holding the stomach in place during everyday movements like bending, coughing, or straining. The diaphragm muscle itself also loses tone with age, and the hiatus can widen. This is why hiatal hernias become increasingly common after age 50.
Pressure From Below
Anything that repeatedly increases pressure inside your abdomen can push the stomach upward through a weakened hiatus. The most significant pressure-related causes include:
- Obesity: Excess abdominal fat creates constant upward pressure on the stomach. Research on over 1,300 patients found the probability of having a hiatal hernia increased at every level of body mass index, with each step up in weight category raising the risk significantly.
- Pregnancy: The growing uterus pushes abdominal organs upward and increases pressure on the diaphragm.
- Chronic coughing: Conditions like COPD or long-term smoking cause repeated, forceful coughing that strains the muscles around the hiatus over months or years.
- Chronic constipation: Regular straining during bowel movements generates spikes of abdominal pressure directed upward.
- Heavy lifting: Repeated heavy lifting, especially with improper breathing technique, forces pressure toward the diaphragm.
These causes don’t usually trigger a hernia overnight. They work gradually, stretching the hiatal opening a little more each time until the stomach finds room to slide through.
Why Obesity Matters More Than You’d Think
Weight deserves special attention because it does double duty. Excess body fat raises baseline abdominal pressure around the clock, not just during activity. A study comparing patients across weight categories found that being overweight was an independent risk factor for hiatal hernia, meaning it raised the risk on its own regardless of other factors. The same study linked higher BMI to esophagitis (inflammation of the esophagus), largely because the hernia that obesity promotes also disrupts the body’s natural acid barrier.
Losing weight is one of the most effective ways to reduce both the symptoms and progression of a hiatal hernia. Even moderate weight loss can relieve the upward pressure on the stomach enough to improve reflux.
Smoking and the Diaphragm
Smoking contributes through two pathways. First, it weakens the lower esophageal sphincter, the ring of muscle at the bottom of the esophagus that normally helps keep stomach contents where they belong. Second, and more directly relevant, smoking often leads to a chronic cough that repeatedly stresses the muscles surrounding the hiatal opening. The combination of weakened tissues and constant mechanical strain makes the area especially vulnerable.
Congenital and Structural Causes
Some people are born with a larger-than-normal hiatal opening, which makes herniation easier later in life. Congenital diaphragmatic hernias, where the diaphragm doesn’t form completely before birth, are a separate and more serious condition typically diagnosed in newborns. In about 10 to 15 percent of these cases, the hernia is part of a broader genetic syndrome. Isolated congenital diaphragmatic hernia, however, is rarely inherited, and most affected families have only one case.
For adults, having a naturally wider hiatus is a predisposing factor that may not cause problems until age, weight gain, or another trigger tips the balance.
Hernias in the Upper Abdominal Wall
When people search for a “hernia in the stomach,” they sometimes mean a bulge in the upper abdominal area rather than inside the diaphragm. Epigastric hernias occur when tissue pushes through a weak spot in the abdominal wall between the breastbone and the belly button. These are most common in obese patients and middle-aged men, and share many of the same pressure-related risk factors: chronic coughing, constipation, and structural weaknesses in the connective tissue. They usually contain only a small amount of fat rather than stomach tissue, though in rare cases abdominal organs can be involved.
When Surgery Becomes Necessary
Most sliding hiatal hernias don’t need surgery. They’re managed with lifestyle changes like weight loss, eating smaller meals, not lying down after eating, and elevating the head of the bed. Medications that reduce stomach acid can control reflux symptoms effectively for many people.
Paraesophageal hernias are a different story. Current surgical guidelines recommend repair for all paraesophageal hernias that cause symptoms, because of the risk of serious complications like the stomach twisting on itself (volvulus), losing blood supply (strangulation), or becoming trapped in the chest (incarceration). An acute paraesophageal hernia with chest pain, vomiting, difficulty swallowing, or signs of infection is a surgical emergency.
For completely asymptomatic paraesophageal hernias found incidentally, the decision is less clear-cut. Surgeons weigh your age, overall health, and the risks of the operation itself. A younger, healthy person with a large paraesophageal hernia may benefit from elective repair to prevent a future emergency, while an older patient with significant health problems might be better served by careful monitoring.