A hiatal hernia happens when part of your stomach pushes up through the diaphragm, the large muscle that separates your chest from your abdomen. The most common cause is repeated or sustained pressure inside your abdomen that gradually weakens the opening (called the hiatus) where your esophagus passes through the diaphragm. Age plays a major role too: about 16.5% of people under 50 have one, but that number climbs to over 35% in people past 80.
Most hiatal hernias develop slowly, driven by a combination of factors rather than a single event. Here’s what’s actually going on inside your body and which risk factors matter most.
How the Diaphragm Weakens Over Time
Your diaphragm has a small opening, the hiatus, that your esophagus threads through on its way to your stomach. Muscles and connective tissue around this opening keep things snug. But like any tissue in the body, these structures lose elasticity and strength with age. The collagen fibers that hold the hiatus tight gradually break down, and the opening slowly widens.
This is why prevalence rises so predictably with each decade of life. A study published in Gastroenterology Report found that hiatal hernias affected 24.6% of people aged 51 to 60, 31.3% of those 61 to 70, and 37.3% of people over 81. The trend is nearly linear: the older you get, the weaker that opening becomes, and the easier it is for the top of your stomach to slide upward.
Pressure From Below: The Primary Driver
The single biggest mechanical cause is repeated or chronic pressure pushing upward against the diaphragm from inside your abdomen. Think of it like a slow, persistent force stretching a rubber band. Over months and years, the hiatus gradually gives way. The most common sources of that pressure include:
- Chronic coughing or sneezing, which repeatedly spikes abdominal pressure
- Straining during bowel movements, especially from long-term constipation
- Frequent vomiting, which forces the stomach upward against the diaphragm
- Heavy lifting or intense exercise, particularly movements that involve bearing down
None of these activities cause a hiatal hernia from a single episode. It’s the chronic, repetitive nature that matters. Someone who strains on the toilet occasionally faces far less risk than someone dealing with constipation for years.
Obesity and Excess Weight
Carrying extra weight around your midsection creates constant upward pressure on the diaphragm, even when you’re just sitting or lying down. Chronic obesity, defined as a BMI greater than 30, is one of the most well-established risk factors. The excess abdominal fat physically compresses the stomach and pushes it toward the hiatus.
This isn’t a temporary or occasional force like coughing. It’s a 24-hour pressure that never lets up, which is part of why it’s so effective at weakening the diaphragm over time. Losing weight can reduce that pressure, though it won’t reverse a hernia that’s already formed.
Pregnancy and Childbirth
Pregnancy creates a similar pressure dynamic. As the uterus expands, it pushes abdominal organs upward, compressing the stomach against the diaphragm. This makes pregnancy a significant risk factor for hiatal hernia, particularly during the second and third trimesters when the uterus is large enough to meaningfully increase intra-abdominal pressure.
The physical strain of childbirth itself adds another spike of intense abdominal pressure. For many women, hernias that develop during pregnancy are small and cause no symptoms. But for some, especially those who’ve had multiple pregnancies, the cumulative effect can produce a hernia that persists after delivery.
Trauma and Injury
While most hiatal hernias develop gradually, a sudden traumatic injury can cause one almost instantly. During severe blunt abdominal trauma, like a high-speed car accident, a multi-story fall, or a crush injury, intra-abdominal pressure can spike to extreme levels. That sudden force transfers directly through the abdominal organs to the diaphragm, tearing or rupturing the muscle.
Penetrating injuries, like a stab wound to the torso, can also lacerate the diaphragm directly. These traumatic hernias are different from the typical age-related kind. They’re often harder to detect initially because the tears can be small, and symptoms may not appear until abdominal organs gradually migrate through the defect over weeks or months. Previous surgeries on the esophagus or upper stomach can also weaken the area around the hiatus and increase the risk of hernia formation later.
Two Types, Same Basic Cause
There are two main types of hiatal hernia, and while the underlying forces are similar, the anatomy differs.
A sliding hiatal hernia (Type I) is by far the most common, accounting for roughly 95% of cases. In this type, the junction where the esophagus meets the stomach slides upward through the hiatus. It often moves up and down, slipping back into place when pressure decreases. This is the type most associated with acid reflux.
A paraesophageal hernia (Types II through IV) is less common but more concerning. Here, part of the stomach pushes up alongside the esophagus through the hiatus, while the junction itself stays in place. In severe cases, a large portion of the stomach (or rarely, other organs) can migrate into the chest cavity. These are more likely to cause complications like restricted blood flow to the herniated tissue.
Both types result from the same combination of diaphragm weakening and abdominal pressure. The difference is mainly in where the tissue pushes through and how it positions itself once it’s there.
Who’s Most at Risk
Several factors stack on top of each other. You’re at higher risk if you’re over 50, carry significant extra weight, have a chronic cough (from smoking, asthma, or other lung conditions), or deal with ongoing constipation. Smoking contributes both through the chronic coughing it causes and through its broader effects on tissue integrity throughout the body.
Genetics likely play a role too, since some people are born with a larger-than-average hiatus or with connective tissue that’s inherently less resilient. If you have a family history of hiatal hernias, you may be starting with a structural disadvantage that makes all the other risk factors more impactful. The combination of an aging diaphragm, sustained abdominal pressure, and individual anatomy is what ultimately determines whether a hernia develops and how large it becomes.