A hiatal hernia happens when part of your stomach pushes up through a small opening in your diaphragm, the sheet of muscle separating your chest from your abdomen. The cause is almost always a combination of a weakened diaphragm and repeated pressure from below. For most people, this develops slowly over many years rather than from a single event.
How the Diaphragm Weakens Over Time
Your esophagus passes through a narrow gap in your diaphragm called the esophageal hiatus, which is only about 2 centimeters long. A band of connective tissue anchors your esophagus in place and keeps the top of your stomach firmly below the diaphragm. When that connective tissue stretches out or the surrounding muscle loses tone, the opening gradually widens, and the top of your stomach can slip upward through the gap.
This is why hiatal hernias become far more common with age. The muscle fibers and connective tissue around the hiatus lose elasticity over the decades, just like tissue elsewhere in the body. A large imaging study that followed over 3,200 people found the prevalence of hiatal hernias climbed steeply by decade: about 2.4% in people in their 50s, 7% in their 60s, 14% in their 70s, and nearly 17% in people 80 and older. That steady increase reflects the cumulative wear on the diaphragm over a lifetime.
Pressure From Below: The Main Trigger
A weakened hiatus creates an opportunity, but it usually takes repeated upward pressure in the abdomen to push the stomach through. Anything that increases abdominal pressure can contribute, and the effects add up over years. Common sources include:
- Chronic coughing or vomiting, which creates sudden, forceful spikes in abdominal pressure
- Straining during bowel movements, especially with chronic constipation
- Heavy lifting, particularly with improper breathing technique
- Intense or repetitive exercise that engages the core under load
For men specifically, heavy physical labor has been identified as an independent risk factor. The repeated bearing down over years of manual work gradually stretches the hiatus wider.
Obesity and Body Weight
Carrying excess weight is one of the strongest modifiable risk factors. Extra abdominal fat creates constant upward pressure on the diaphragm, not just during exertion but all the time. Research comparing people across weight categories found that the probability of a hiatal hernia increased at each level of BMI, with the association reaching statistical significance. Obesity is also strongly linked to esophagitis (inflammation of the esophagus), largely because hiatal hernias make acid reflux worse.
This matters practically: losing weight can reduce the pressure driving the hernia upward and often improves reflux symptoms, even if the hernia itself doesn’t fully resolve.
Pregnancy
Pregnancy raises abdominal pressure substantially, especially in the third trimester as the uterus expands. The forces are similar to those from obesity but concentrated into a shorter time frame. Some hernias that develop during pregnancy resolve afterward as pressure normalizes, though in women who already had a weakened hiatus, the stretching can be permanent. Multiple pregnancies compound the effect.
Two Types, Same Root Cause
Most hiatal hernias (roughly 70% in population studies) are the sliding type. The junction where your esophagus meets your stomach slides up through the widened hiatus, then slides back down. This type tends to come and go, which is why some people notice symptoms only at certain times, like after a large meal or when lying down.
The less common type is called paraesophageal, meaning “beside the esophagus.” Here, the esophagus stays in place, but a portion of the stomach bulges up alongside it, forming a pouch next to the esophagus inside the chest cavity. This type is more concerning because the bulging portion can become trapped or have its blood supply pinched off. Both types develop from the same underlying process of a widened hiatus and upward pressure, but paraesophageal hernias tend to be larger and more likely to need treatment.
Genetics and Connective Tissue
Some people are structurally more vulnerable. Research has identified specific genetic risk locations associated with hiatal hernias, and people with connective tissue disorders like Ehlers-Danlos syndrome have a well-known predisposition to hernias of all types. Even outside of named disorders, people vary in their collagen composition. Studies have found that people who develop hernias tend to have lower ratios of the stronger type of collagen to the more flexible type, making their connective tissue less resistant to stretching.
In rare cases, a baby can be born with a hiatus that’s unusually large from the start. These congenital hiatal hernias typically show up early in life rather than in middle age. But for most adults, genetics plays more of a background role, setting the threshold for how much wear and tear the hiatus can handle before it gives way.
Injury and Surgery
A direct injury to the diaphragm, whether from trauma or from a previous abdominal surgery, can create or worsen a weak point at the hiatus. Surgeries in the upper abdomen sometimes alter the anatomy enough to make a hernia more likely down the road. These cases are less common than the gradual, age-related type, but they explain why hiatal hernias occasionally appear in younger people with no other obvious risk factors.
Why It Usually Isn’t Just One Thing
The pattern that emerges across the research is that hiatal hernias rarely have a single cause. They develop when a person’s individual vulnerability (age, genetics, connective tissue quality) meets enough accumulated stress (body weight, physical strain, coughing, pregnancy). Someone with strong connective tissue might lift heavy objects for decades without issue. Someone with naturally stretchier tissue might develop a hernia with far less provocation. The condition is the endpoint of multiple forces working together over time, which is why it’s so much more common in older adults and why pinpointing one specific trigger is usually impossible.