As of 2015, the exact cause of hiatal hernias is unclear. Possible causes include a large hiatus at birth, injury to the diaphragm or consistent, severe pressure on area muscles, such as when a person vomits, coughs or lifts something heavy, states Mayo Clinic.
Other factors that possibly contribute to hiatal hernias are pressure on the stomach and age-related changes in the diaphragm, Mayo Clinic explains.
The diaphragm is a large, rounded muscle between the abdomen and chest cavity. The hiatus is an opening in the diaphragm through which the esophagus passes into the stomach. When the muscle tissue around the hiatus weakens, the upper stomach protrudes through the diaphragm into the chest cavity, creating the hernia, according to Mayo Clinic.
Some people are born with a larger hiatus opening, states WebMD. The larger opening makes it easier for the stomach to move through the hiatus, according to Healthline.