Heartburn is most commonly caused by gastro-oesophageal reflux, meaning stomach contents move backwards through the lower oesophageal sphincter into the oesophagus. The stomach contains acid and digestive substances needed for digestion, but the oesophageal lining is not designed for repeated exposure to these contents. When reflux reaches the oesophagus, it can stimulate sensory nerves and produce the characteristic burning sensation. Occasional reflux is common and does not necessarily mean disease. When reflux becomes recurrent, troublesome or associated with complications, it may be classified as GORD. The central physiological problem is therefore not simply that the stomach produces acid, but that gastric contents are able to enter an area where they are not normally present.
The lower oesophageal sphincter is a major component of the anti-reflux barrier. It normally remains closed between swallows and opens when food passes from the oesophagus into the stomach. Reflux can occur when the sphincter is weak or undergoes transient relaxations that are not associated with swallowing. The diaphragm surrounds the oesophageal opening and contributes additional support. A hiatus hernia can alter this anatomy by allowing the upper part of the stomach to move into the chest through the diaphragmatic opening, which can make reflux more likely or worsen existing GORD. These mechanical factors help explain why reflux is influenced by anatomy, pressure and body position.
Meals and eating patterns can influence heartburn because stomach distension and the presence of food can increase opportunities for reflux. Large meals can produce greater gastric distension than smaller meals, and lying down soon after eating removes the assistance of gravity. Eating within a few hours of bedtime is therefore a common contributor to nocturnal symptoms.
High-fat foods can be associated with reflux symptoms in some people, while chocolate, caffeine, alcohol, mint, spicy foods and acidic foods are commonly reported triggers. These are associations rather than universal causes: a food that reliably triggers symptoms in one individual may have little effect on another, so unnecessary blanket dietary restriction is not always appropriate.
Increased pressure within the abdomen can favour upward movement of gastric contents. Overweight or obesity is associated with a higher risk of GORD, and weight reduction can improve symptoms in people who are overweight or have obesity. Pregnancy can also increase reflux through a combination of increased abdominal pressure and hormonal effects on gastrointestinal physiology. Tight clothing is sometimes blamed for heartburn, but the evidence and importance vary compared with better-established factors such as body weight, meal timing and anatomical reflux mechanisms. The relationship between physical pressure and reflux is best understood as one factor among several rather than a single universal explanation for every episode.
Smoking can contribute to reflux and can make symptoms worse. Tobacco exposure can affect the function of the lower oesophageal sphincter and other protective mechanisms, while coughing and other effects of smoking may also alter pressure within the chest and abdomen. Second-hand smoke has also been identified as a potential factor affecting reflux. Alcohol is another commonly reported trigger, although the mechanism and symptom response vary between individuals. Reducing or eliminating a trigger is most useful when there is a consistent relationship between exposure and symptoms. These lifestyle factors can interact with other causes, so removing one trigger does not necessarily eliminate heartburn if anatomical or physiological reflux remains.
Medicines can sometimes cause or aggravate reflux symptoms. Examples identified in clinical references include benzodiazepines and other sedating medicines, calcium-channel blockers, certain asthma medicines, NSAIDs and tricyclic antidepressants. Medication effects can arise through changes in sphincter function, gastrointestinal motility or mucosal sensitivity. A medicine that coincides with the onset of heartburn should not automatically be stopped, because prescribed medicines may be essential for another condition. Instead, the prescribing clinician or pharmacist can assess whether the medicine, dose, timing or an alternative treatment may be relevant. The possibility of medication-related reflux is particularly important when symptoms begin after a new medicine is introduced.
Not every cause of chest burning is reflux. Heartburn can be confused with dyspepsia, gastritis, peptic ulcer disease, oesophageal inflammation, musculoskeletal pain and cardiac disease. Heartburn is specifically associated with a burning sensation behind the breastbone, whereas dyspepsia primarily involves upper-abdominal symptoms. A stomach ulcer is a mucosal lesion caused most commonly by H. pylori infection or NSAID exposure and can produce upper-abdominal burning rather than classic retrosternal heartburn. Cardiac chest pain can also resemble heartburn, so new or unexplained chest discomfort should not be self-diagnosed solely from its burning quality.
Preventing heartburn therefore focuses on reducing the circumstances that allow reflux or amplify its symptoms rather than trying to eliminate stomach acid completely. Useful measures include avoiding meals for at least two to three hours before lying down, losing excess weight when appropriate, stopping smoking, elevating the upper body during sleep for nocturnal symptoms and identifying individual dietary triggers. Medicines that reduce gastric acid can be useful when symptoms are frequent or when GORD is present, but they do not necessarily prevent the physical act of reflux. Persistent or frequent heartburn should be medically assessed because it may represent GORD requiring structured treatment or an alternative condition requiring different management.
