What Is Heartburn and What Causes It?

Heartburn, Reflux & Indigestion: The Complete Guide

What Is Heartburn? (Quick Answer)

Heartburn is a burning sensation felt in the chest, typically behind the breastbone, that occurs when stomach contents move upward into the esophagus. Despite the name, heartburn has nothing to do with the heart. The sensation arises because the sensitive lining of the esophagus is exposed to acidic stomach contents it is not designed to tolerate.

Quick Summary

  • Heartburn is a symptom — the burning sensation caused by acid moving into the esophagus
  • The primary cause is a weakened or malfunctioning lower esophageal sphincter (LES)
  • Heartburn is not always caused by excess stomach acid — the underlying picture is more complex
  • Risk factors include obesity, hiatal hernia, delayed gastric emptying, and certain foods and medications
  • Occasional heartburn is extremely common; frequent heartburn may warrant further attention

Heartburn affects an estimated 20% of adults in Western countries on a regular basis, making it one of the most common digestive complaints worldwide. Understanding what actually causes it — beyond the oversimplified "too much acid" explanation — is the foundation for addressing it effectively.

What Happens During Heartburn

To understand heartburn, it helps to understand how the digestive system normally works. When you swallow, food travels down the esophagus and passes through a muscular valve at the bottom called the lower esophageal sphincter (LES). The LES opens to allow food into the stomach, then closes tightly to keep stomach contents — including digestive acids — from flowing back up.

When the LES doesn't close properly, or relaxes at the wrong time, stomach contents can move backward into the esophagus. The esophageal lining is not equipped to handle acidic contents the way the stomach lining is. When acid contacts the esophagus, it triggers the burning sensation we call heartburn.

According to the Mayo Clinic, heartburn typically causes a burning feeling in the chest that may rise toward the throat, and often occurs after eating, when bending over, or when lying down.

The Root Causes of Heartburn

Heartburn is not caused by a single factor. Research published in PMC (NIH) identifies multiple contributing mechanisms:

1. Lower Esophageal Sphincter (LES) Dysfunction

The LES is the primary barrier between the stomach and esophagus. Two distinct types of LES problems contribute to reflux and heartburn:

  • Reduced resting LES pressure — a chronically weakened sphincter that allows acid to pass upward more easily
  • Transient LES relaxations (TLESRs) — brief, spontaneous relaxations of the LES that are not triggered by swallowing. These are the most common mechanism behind both occasional reflux and chronic GERD. They increase in frequency after meals and when the stomach is distended.

2. Impaired Esophageal Mucosal Barrier

The esophageal lining has its own protective barrier — a layer of tightly joined cells that normally prevents acid from penetrating to the deeper, nerve-rich layers beneath. When this barrier is compromised, acid can diffuse between cells and stimulate pain-sensing nerves even during what would otherwise be minor reflux events.

Research published in PMC has identified impaired esophageal mucosal barrier function as a key factor in why some people experience significant heartburn symptoms even when acid exposure appears normal on testing. This helps explain why heartburn intensity does not always correlate directly with the amount of acid present.

3. Delayed Gastric Emptying

When the stomach takes longer than normal to empty its contents into the small intestine, pressure builds inside the stomach. This increased gastric pressure can force contents upward through the LES, increasing the frequency and severity of reflux events.

4. Increased Intra-Abdominal Pressure

Anything that increases pressure inside the abdominal cavity can push stomach contents toward the LES, overwhelming its ability to remain closed. Common causes include:

  • Obesity — excess abdominal weight increases resting gastric pressure
  • Pregnancy — the growing uterus compresses abdominal contents
  • Tight clothing around the abdomen
  • Bending forward or lying down after eating
  • Heavy lifting

5. Hiatal Hernia

A hiatal hernia occurs when part of the stomach pushes upward through the diaphragm into the chest cavity. The diaphragm normally helps support the LES and reinforces its barrier function. When a hiatal hernia is present, this support is weakened, making reflux more likely. According to Cleveland Clinic, hiatal hernia is a common contributing factor in GERD.

6. Esophageal Hypersensitivity

Some individuals experience significant heartburn symptoms even when actual acid exposure is minimal. This is known as esophageal hypersensitivity — where pain-sensing nerves in the esophagus become sensitized and respond to stimuli that would not normally trigger discomfort. Recent research published in Physiological Reports (2025) confirms that esophageal sensitivity, rather than acid volume alone, plays a significant role in heartburn severity for many people.

The Misconception About Stomach Acid

For decades, heartburn was explained almost entirely as a problem of too much stomach acid. The logic seemed straightforward — acid causes burning, so reducing acid should solve the problem. This reasoning gave rise to antacids, H2 blockers, and proton pump inhibitors (PPIs), all of which work by neutralizing or suppressing acid production.

The emerging research paints a more complete picture. Stomach acid is not the enemy — it is essential for protein digestion, killing pathogens, and activating digestive enzymes. The problem in most cases is not how much acid is produced, but where it ends up. When the LES malfunctions, acid that belongs in the stomach moves into the esophagus, where it does not belong.

Furthermore, research suggests that many individuals experiencing frequent heartburn actually have normal or reduced stomach acid, but reflux events due to LES dysfunction, increased gastric pressure, or mucosal barrier compromise. Simply suppressing acid in these individuals addresses symptoms without addressing the underlying dysfunction — which is part of why many people find their relief from acid-suppressing medications diminishes over time.

Related article: Why Do Antacids and PPIs Stop Working — and What Then?

Common Risk Factors for Heartburn

Beyond the direct mechanisms, several factors increase the likelihood of experiencing heartburn:

  • Overweight or obesity — one of the most consistently documented risk factors, due to increased intra-abdominal pressure and its effects on LES function
  • Diet — certain foods directly affect LES tone or gastric acid secretion (covered in depth in What Foods Cause Heartburn?)
  • Smoking — reduces LES resting pressure and impairs esophageal clearance
  • Certain medications — including NSAIDs, calcium channel blockers, some antidepressants, and bisphosphonates
  • Stress — influences gastric acid secretion, gastric motility, and esophageal sensitivity
  • Pregnancy — hormonal changes relax smooth muscle including the LES, and physical pressure increases as pregnancy progresses
  • Age — LES tone and esophageal motility can decline with age

What Heartburn Feels Like — and What It Doesn't

The classic description of heartburn is a burning sensation in the chest, behind the breastbone, that may rise toward the throat or mouth. It often occurs within 30–60 minutes of eating, and tends to worsen when lying down or bending over. Some people experience a sour or bitter taste in the mouth, known as regurgitation.

Heartburn can occasionally be confused with cardiac chest pain, which is one reason why persistent or severe chest discomfort should always be evaluated by a healthcare professional to rule out cardiac causes. True heartburn typically improves with antacids or positional changes, which can help differentiate it from cardiac pain — but this distinction should always be confirmed by a clinician.

Less commonly recognized symptoms that can be associated with reflux include:

  • Chronic cough or hoarseness, particularly in the morning
  • Sensation of a lump in the throat
  • Chronic throat clearing
  • Worsening of asthma symptoms
  • Dental erosion from acid exposure

When Occasional Heartburn Becomes a Pattern Worth Addressing

Occasional heartburn — after a large meal, a glass of wine, or a late dinner — is extremely common and experienced by most people at some point. It does not necessarily indicate an underlying problem.

According to the National Library of Medicine, heartburn that occurs two or more times per week, disrupts daily life or sleep, or does not respond to basic dietary modifications is worth discussing with a healthcare professional. This frequency is generally used as a threshold for clinical concern and further evaluation.

A healthcare professional can help distinguish occasional heartburn from GERD or other conditions that may require specific evaluation, and can provide appropriate guidance based on your individual situation.

How Silver Fern™ Brand Approaches Upper GI Comfort

Silver Fern™ Brand's approach to upper GI support focuses on the underlying digestive environment rather than suppressing acid. Our products are designed to support mucosal barrier integrity, healthy gastric motility, and balanced digestive function — the same factors that emerging research identifies as central to the heartburn picture.

*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.

Key Takeaways

  • Heartburn is a burning sensation caused by stomach contents entering the esophagus — not a heart condition
  • The primary cause is lower esophageal sphincter (LES) dysfunction, particularly transient LES relaxations
  • Impaired esophageal mucosal barrier function and esophageal hypersensitivity play important roles that are often overlooked
  • Heartburn is not always caused by excess stomach acid — it is more often a problem of where acid ends up than how much is produced
  • Common risk factors include obesity, hiatal hernia, delayed gastric emptying, certain foods, smoking, stress, and some medications
  • Frequent heartburn occurring two or more times per week warrants a conversation with a healthcare professional

Sources and References

This article is for educational purposes only. It does not constitute medical advice and is not a substitute for consultation with a qualified healthcare professional. If you are experiencing frequent or severe chest discomfort, please seek medical evaluation to rule out cardiac and other causes.