A hiatal hernia happens when part of your stomach pushes upward through the diaphragm, the sheet of muscle separating your chest from your abdomen. The diaphragm has a small opening called the hiatus where your esophagus passes through to connect to your stomach. When the tissue around that opening weakens or stretches, the stomach can slide or bulge into the chest cavity. This is extremely common: about 20% of the general U.S. population has one, and that number climbs to 50% of people over 50 and 70% of people over 70.
Several factors, from aging to genetics to body weight, contribute to this weakening. Most people develop a hiatal hernia from a combination of causes rather than a single event.
How the Diaphragm Weakens With Age
The single biggest driver of hiatal hernias is age-related wear on the diaphragm and the connective tissue that anchors your esophagus in place. A band of tissue called the phrenoesophageal ligament holds the junction between your esophagus and stomach snugly within the diaphragmatic opening. Over decades, this tissue loses elasticity. The muscle fibers of the diaphragm itself also become less flexible. As both structures loosen, the hiatus gradually widens, and the upper portion of the stomach can slip through.
This is why hiatal hernias track so closely with age. The sharp jump from 50% prevalence at age 50 to 60% at age 60 to 70% at age 70 reflects a slow, cumulative process rather than a sudden event. Many people have a small hiatal hernia for years without knowing it.
Repeated Pressure on the Abdomen
Anything that repeatedly or chronically pushes pressure upward against the diaphragm can force the stomach through the hiatus. Think of the diaphragm as a ceiling with a weak spot: enough upward force, applied often enough, will eventually push something through. Common sources of this pressure include:
- Chronic coughing from conditions like COPD, asthma, or long-term smoking
- Straining during bowel movements due to chronic constipation
- Heavy lifting or frequent vomiting, both of which spike abdominal pressure
- Pregnancy, which combines hormonal changes that relax connective tissue with months of increasing mechanical pressure from the growing uterus
These factors are especially likely to cause a hernia in someone whose diaphragm tissue is already loosening with age. A younger person with strong connective tissue can usually absorb the same pressure without anything shifting.
Obesity and Excess Body Weight
Carrying extra weight around the abdomen creates constant upward pressure on the diaphragm. A meta-analysis found that people with a BMI above 25 had roughly twice the odds of developing a hiatal hernia compared to those at a normal weight, and the risk increased as BMI climbed higher. Visceral fat, the deep fat packed around your organs, is particularly problematic because it sits directly below the diaphragm and presses on the stomach continuously, not just during exertion.
Weight loss can reduce this pressure, though it won’t reverse a hernia that has already formed. It can, however, reduce the severity of symptoms like acid reflux.
Genetics and Family History
Some people are born with a wider hiatus or weaker connective tissue at the diaphragm, making them predisposed to hernias regardless of lifestyle. A study tracking 38 members across five generations of a single family found that 23 of them had radiological evidence of a hiatal hernia. No affected individual was born to unaffected parents, and the pattern pointed to autosomal dominant inheritance, meaning a single copy of the gene from one parent is enough to pass on the risk.
Familial hiatal hernia is considered rare, but it may simply be underreported. If multiple close relatives have been diagnosed, your own risk is likely elevated. In rare cases, babies are born with a congenital diaphragmatic defect that allows a hiatal hernia from birth, though this is a distinct condition typically identified early in life.
Smoking
Smoking contributes to hiatal hernias through at least two pathways. The more obvious one is chronic coughing, which hammers the diaphragm with repeated pressure spikes. But a genetic study using a method called Mendelian randomization found that smoking intensity itself is independently linked to a higher risk of diaphragmatic hernia, with heavier smokers facing greater risk. The estimated increase was about 21% to 26% higher odds per unit of smoking intensity. This suggests that compounds in cigarette smoke may directly weaken connective tissue or impair muscle repair in the diaphragm, beyond just the mechanical effect of coughing.
Prior Abdominal or Chest Surgery
Hiatal hernias can develop as a complication after surgeries that alter the anatomy around the diaphragm. Operations to remove part of the esophagus or stomach are the most common culprits. One review described post-surgical hiatal hernia as “an underreported complication,” with cumulative rates reaching as high as 26% in patients who had their esophagus removed, even when they had no symptoms. Minimally invasive surgical approaches carried a higher rate (around 4.5%) than traditional open surgery (around 1%), likely because the less invasive technique leaves fewer internal adhesions, the natural scar tissue that helps hold organs in place.
About one-third of these post-surgical hernias develop within the first 90 days, before adhesions have had time to form. When abdominal organs herniate into the chest after surgery, the situation can become a medical emergency if bowel tissue gets trapped and loses its blood supply.
Two Types, Two Mechanisms
Not all hiatal hernias form the same way, and the underlying cause can determine which type you develop. In a sliding hiatal hernia, the most common type, the junction between your esophagus and stomach slides upward through the hiatus. This is typically driven by the age-related tissue loosening and pressure factors described above. The stomach moves up and down, often worsening when you lie down or bend over.
In a paraesophageal hernia, the esophagus stays in place but a portion of the stomach bulges up beside it through a weakness in the connective tissue anchoring the esophagus. This type is more closely linked to a structural defect in the phrenoesophageal ligament itself. Some people develop a combination of both types when general tissue looseness at the hiatus coexists with a specific weak point in the connective tissue. Paraesophageal hernias are less common but carry a higher risk of complications because the stomach tissue can become trapped or twisted.
Why Multiple Causes Usually Overlap
In practice, hiatal hernias rarely have a single clean explanation. A typical scenario involves someone whose diaphragm tissue has gradually weakened with age, who carries some extra abdominal weight, and who has a chronic cough or history of straining. Each factor alone might not be enough, but together they cross a threshold. This is why the condition becomes so much more common in older adults: time allows multiple contributing factors to accumulate and compound. Even people with a genetic predisposition often don’t develop a noticeable hernia until middle age or later, when the tissue has had decades to stretch.