How Does a Hiatal Hernia Happen: Causes and Types

A hiatal hernia happens when part of the stomach pushes upward through the hiatus, the natural opening in the diaphragm where the esophagus passes through on its way to the stomach. The diaphragm normally hugs the esophagus tightly at this point, keeping everything in its proper compartment. When the tissues around that opening weaken or stretch, the stomach can slide or roll into the chest cavity. Three broad forces drive the process: rising pressure inside the abdomen, deterioration of the connective tissue that anchors the esophagus to the diaphragm, and structural changes from aging or body composition.

The Four Types

Not all hiatal hernias look the same on imaging or during surgery. They fall into four categories, and the type matters because it shapes both the symptoms you experience and the treatment a surgeon might recommend.

• Type I (sliding): The junction where the esophagus meets the stomach slides upward through the hiatus. This is by far the most common type, originating from the right crus of the diaphragm, and it accounts for the vast majority of diagnosed cases.¹ The hernia often slides up and down depending on body position and breathing, which is why it can be easy to miss on a single snapshot.
• Type II (paraesophageal): The esophagus stays in place, but a portion of the stomach’s upper curve (the fundus) herniates alongside it into the chest. This type is less common but more concerning because the herniated portion can become trapped.
• Type III (mixed): A combination of the first two. Both the esophageal junction and a portion of the fundus have migrated upward. Large Type III hernias can contain a substantial part of the stomach.
• Type IV: An organ other than the stomach, such as the colon or spleen, has also migrated through the hiatus alongside the stomach. These are rare and almost always require surgical repair.

Type I hernias are responsible for most of the reflux-related complaints people associate with the condition. Types II through IV, collectively called paraesophageal hernias, carry a higher risk of mechanical complications like obstruction or volvulus, where the stomach twists on itself.

Pressure From Below

One of the dominant theories explaining how hiatal hernias develop centers on increased pressure inside the abdomen physically forcing the junction between the esophagus and stomach upward through the diaphragm.² Anything that chronically raises intra-abdominal pressure can contribute: obesity, pregnancy, heavy lifting, chronic coughing, or severe constipation with repeated straining.

Obesity deserves special attention here because it does not just add weight. Central fat deposits around the waist create sustained mechanical compression. A study using real-time pressure monitoring showed that both a tight waist belt and increased waist circumference independently pushed the point where the stomach lining meets the esophagus upward into the diaphragmatic hiatus. In people who were already obese, the junction was resting in a displaced position even before any additional external compression was applied.³ The researchers also found that acid exposure just above the stomach lining increased when the belt was on, and the effect was most pronounced in obese subjects. This helps explain why weight gain and hiatal hernias so often go hand in hand, and why age and higher body mass index are consistently flagged as the leading risk factors.¹

Why the Anchoring Tissue Weakens

Pressure alone does not cause a hiatal hernia if the tissues holding everything in place are strong. The esophagus is tethered to the diaphragm by a structure called the phrenoesophageal ligament, a membrane that acts like a collar around the esophagus at the hiatus. When that collar loosens, the stomach can migrate more easily. Researchers studying this ligament found that patients with hiatal hernias had roughly 60% less collagen in their phrenoesophageal ligament compared to people without one, across both the main structural collagen types (type I and type III).⁴ That is a dramatic difference, and it suggests the quality of this ligament is a genuine factor in whether a hernia develops, not just a consequence of already having one.

Collagen naturally breaks down with age, which is one reason hiatal hernias become more common in older adults. The diaphragm’s muscle fibers also lose elasticity over time. Combined with decades of swallowing, breathing, and postural stress on the hiatus, the opening gradually stretches. This slow degradation is why many people develop a hiatal hernia without any dramatic triggering event. There is no single cough or heavy lift that “causes” it. Instead, the tissue has been quietly losing its grip for years, and the hernia eventually appears once the structural deficit reaches a tipping point.

Connective Tissue Disorders and Inherited Risk

Some people are born with connective tissue that is structurally weaker than average, and this can predispose them to hiatal hernias at younger ages. The clearest example involves the Ehlers-Danlos syndromes, a group of inherited conditions affecting collagen and related proteins throughout the body. Patients with Ehlers-Danlos can develop structural problems including hiatal hernias, organ prolapse, and rectal prolapse, alongside functional issues like abnormal gut motility.⁵

The reported prevalence of hiatal hernia in people with hypermobile Ehlers-Danlos syndrome varies quite a bit depending on the study, with some reporting rates as high as 58%. Other studies, however, have found rates closer to the general population, which typically runs between about 2% and 22%.⁶ The proposed explanation is that laxity of the ligaments anchoring the esophagus and stomach makes the junction more prone to displacement, but the evidence is not settled enough to say hiatal hernia is an inevitable feature of these conditions. If you have a connective tissue disorder and experience persistent reflux or difficulty swallowing, it is worth mentioning the possibility to your gastroenterologist, because the hernia may not be the first thing they screen for.

Hiatal Hernias After Bariatric Surgery

This is an underappreciated cause that is becoming more relevant as weight-loss surgeries grow more common. Bariatric procedures fundamentally reshape the stomach anatomy, and that reshaping creates new vulnerability at the hiatus. The altered stomach can migrate through the diaphragmatic opening months or years after the original operation.⁷

After gastric bypass, hiatal hernias can appear long after the initial surgery. In one case series, the average time between the bypass and the hernia diagnosis was almost 12 years, with patients presenting at an average age of around 60. The most common complaint was reflux, and imaging showed the gastric pouch had migrated into the chest.⁸ After sleeve gastrectomy, the timeline tends to be shorter; hernias involving the new tube-shaped stomach appear earlier than they do after bypass.⁹ The takeaway is that anyone who has had bariatric surgery and develops new or worsening reflux, bloating, or regurgitation years later should consider the possibility that a hiatal hernia has developed since the procedure.

How a Hiatal Hernia Causes Reflux

Many people with small sliding hernias have no symptoms at all. But when a hiatal hernia does cause problems, acid reflux is the headline complaint, and the mechanics are worth understanding because they explain why reflux from a hernia can be stubborn and hard to control with medications alone.

Under normal conditions, the lower esophageal sphincter and the diaphragm work as a team. The sphincter is a ring of muscle at the bottom of the esophagus that stays contracted to prevent stomach contents from flowing backward. The diaphragm’s crural fibers wrap around the esophagus at the same point, providing external reinforcement. A sliding hernia separates these two defenses. When the stomach junction slides above the diaphragm, the sphincter loses the backup squeeze from the crural muscle, and its own pressure drops.¹⁰ The hernia sac also acts as a small reservoir that can trap acid above the diaphragm and release it into the esophagus during swallowing.

The result is measurable. Patients with hiatal hernias had esophageal acid exposure roughly twice that of patients without hernias, and they experienced more reflux episodes per hour. Interestingly, the extra reflux was not driven primarily by an increase in transient sphincter relaxations, which is the main reflux mechanism in people without hernias. Instead, the excess reflux came from episodes tied to low resting sphincter pressure, normal swallowing, and straining during periods when the sphincter was weak.¹¹ In other words, the hernia creates a structurally compromised barrier that leaks acid through multiple pathways, not just one.¹²

Complications Beyond Reflux

Chronic acid reflux from a hiatal hernia can lead to esophagitis, Barrett’s esophagus, and stricture formation over time. But the more acute dangers come with larger paraesophageal hernias. When a big portion of the stomach sits above the diaphragm, it can twist (gastric volvulus), lose its blood supply (strangulation), or become trapped and unable to slide back down (incarceration). These are surgical emergencies.

Large hiatal hernias can also develop Cameron ulcers, which are linear erosions that form where the stomach rubs against the diaphragm at the hiatus. These ulcers can bleed silently, causing chronic iron-deficiency anemia, or in rare cases perforate.¹³ If you have a known large hernia and develop unexplained anemia or sudden severe chest or abdominal pain, these possibilities should be on the radar.

How Hiatal Hernias Are Diagnosed

Hiatal hernias are often found incidentally during an upper endoscopy or a barium swallow done for another reason. But neither of those tests is particularly sensitive for smaller hernias, and the hernia may or may not be present at the exact moment the image is captured because sliding hernias come and go with position and breathing.

High-resolution manometry, a pressure-sensing catheter threaded through the nose into the esophagus, has emerged as the most accurate office-based test. One study comparing it to what surgeons actually saw during surgery found it had about 94% sensitivity and 92% specificity for detecting and grading sliding hernias, outperforming both barium swallow and endoscopy.¹⁴ Another study in a predominantly obese population also found manometry more sensitive than barium swallow and endoscopy, though its specificity was lower in that group, around 63%, meaning it sometimes flagged hernias that the surgeon did not confirm.¹⁵ The practical message is that if you have persistent reflux symptoms and an endoscopy was normal, a hiatal hernia has not been ruled out. Manometry can catch what other tests miss.

Lifestyle Measures That Address the Causes

Because obesity and intra-abdominal pressure are central drivers of hiatal hernias, weight loss can make a real difference. Two randomized trials found that losing weight reduced the amount of time acid was present in the esophagus, dropping from about 5.6% to 3.7% in one and from 8.0% to 5.5% in another.¹⁶ Weight loss does not reverse a hernia that has already formed, but it reduces the mechanical pressure that worsens herniation and reflux.

Other lifestyle changes target reflux symptoms more than the hernia itself. Elevating the head of the bed decreased nighttime acid exposure from about 21% to 15% in trials. Avoiding late meals helped too: eating close to bedtime increased supine acid exposure by roughly five percentage points compared to eating earlier.¹⁶ Quitting smoking had a striking effect in normal-weight individuals, with one large cohort study finding more than a fivefold reduction in reflux symptom odds after cessation.¹⁶ None of these measures will close the hiatus, but they reduce the day-to-day burden the hernia puts on your esophagus.

When Surgery Is Recommended

Small sliding hernias that respond to acid-suppression medications and lifestyle changes rarely need surgery. The conversation shifts when symptoms are severe, when medications fail, or when the hernia is a larger paraesophageal type. The established surgical indications are symptomatic paraesophageal hernias, especially those with obstructive symptoms or gastric volvulus, which may require urgent intervention.¹⁷

The standard operation is a laparoscopic fundoplication, where the surgeon wraps part of the stomach’s upper portion around the lower esophagus to recreate the valve. A full 360-degree wrap (Nissen) is usual, though a partial 270-degree wrap (Toupet) is preferred when the esophagus does not contract well, to avoid creating swallowing difficulty.¹⁷ Whether to reinforce the repair with mesh is one of the ongoing debates in this field. Short-term data suggest mesh reduces recurrence, but long-term follow-up has not consistently shown a lasting benefit for biologic mesh, and synthetic mesh carries its own risks, including erosion into the esophagus. The Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) explicitly declined to make an evidence-based recommendation for or against mesh, citing equivocal data and low certainty of evidence.¹⁸

Recurrence after hiatal hernia repair is not uncommon, particularly for larger hernias. Estimates vary, but radiographic recurrence rates after paraesophageal repair range widely depending on how aggressively surgeons look for it on follow-up imaging. This is one reason surgeons tend to reserve surgery for people with clear mechanical symptoms or complications rather than offering it preemptively to everyone with a hernia visible on imaging.

Why Some People Get Hernias and Others Do Not

If you line up a group of sixty-year-olds with the same body weight, some will have a hiatal hernia and some will not. The explanation almost certainly lies in the interaction between the mechanical stresses covered earlier and individual variation in connective tissue quality. Two people can carry the same amount of abdominal fat, but the one whose phrenoesophageal ligament has lower collagen density will develop a hernia sooner. Genetics, smoking history (which accelerates collagen breakdown throughout the body), hormonal changes, and prior surgeries all feed into how resilient that tissue is at any given age.

This is also why hiatal hernias can appear in lean, young, otherwise healthy people who do not fit the typical risk profile. When they do, it is worth considering whether an underlying connective tissue condition is at play, particularly if there are signs elsewhere in the body such as joint hypermobility, stretchy skin, or a family history of hernias and prolapse. The hernia in that context is not a standalone problem but a clue to a broader pattern of tissue fragility.