A hiatus (hiatal) hernia happens when the opening in the diaphragm (the hiatus) becomes too loose or weak, allowing part of the stomach to slip up into the chest.

Main things that cause a hiatus hernia

These are not always one‑to‑one “causes”, but well‑known factors that make it more likely you’ll develop one.

  • Age‑related weakening of the diaphragm muscle, especially over 50.
  • Constant or sudden increases in pressure inside the abdomen, for example:
* Heavy lifting or straining (including in the gym or with physical work).

* Frequent or hard coughing (such as with chronic lung disease or long‑term smoking).

* Straining on the toilet with long‑term constipation.

* Repeated vomiting or very forceful sneezing.
  • Obesity or significant excess weight around the abdomen, which constantly pushes upwards on the diaphragm.
  • Pregnancy, due to the growing uterus raising pressure in the abdomen.
  • Injury or surgery in the area of the diaphragm or oesophagus (for example, after trauma or certain operations).
  • Being born with a naturally large hiatus (the opening in the diaphragm is bigger than usual).
  • General tissue laxity with age or certain spine/posture problems such as scoliosis, which can change pressure and angles in the chest and abdomen.

How doctors often explain it

  • The diaphragm is a sheet of muscle that separates the chest from the abdomen, with a small hole (hiatus) where the oesophagus passes through.
  • Over time, or under repeated strain, that opening can stretch or the supporting tissues can weaken.
  • When that happens, part of the stomach can push up through the gap, especially when you bend, lift, cough, or lie down after eating.

A simple picture many people find helpful is to imagine a drawstring around a tube: if the drawstring loosens or you keep pushing from below, some of what’s underneath can slide upward.

Is it something you caused?

Most people have a mixture of things they can’t control (like age, anatomy, and genetics) and things they can (like weight, long‑term constipation, heavy lifting technique, or smoking‑related chronic cough).

So it’s usually not “your fault”, but working on modifiable factors can help symptoms and may reduce progression (for example, weight loss if needed, treating constipation, avoiding very heavy straining, and managing chronic cough with a clinician).

When to get checked

You should seek medical advice urgently if you have any of the following with suspected or known hiatus hernia:

  • Difficulty or pain when swallowing
  • Unexplained weight loss
  • Vomiting blood or black, tarry stools
  • Severe chest or upper abdominal pain, sudden breathlessness, or feeling very unwell

For ongoing heartburn, regurgitation, or upper‑abdominal discomfort lasting more than a few weeks, it’s also sensible to see a doctor or gastroenterologist for assessment. Forum‑style note

Many people in online discussions mention that they only discovered their hiatus hernia during tests for long‑standing “acid reflux” or chest discomfort, and were surprised because they’d had it for years without knowing.

TL;DR:
What causes a hiatus hernia is usually a combination of a weakened diaphragm opening plus repeated or sustained pressure from inside the abdomen (ageing, obesity, coughing, straining, pregnancy, heavy lifting, or prior injury/surgery), and in some people a naturally larger opening from birth.

Information gathered from public forums or data available on the internet and portrayed here.