The Short Answer

Think of it as a chain of cause and effect.

Acid reflux is the mechanical event. Stomach contents travel backward past the lower esophageal sphincter into the esophagus. This is the thing that physically happens.

Heartburn is one possible consequence of that event. The FDA defines it as an uncomfortable, burning feeling in the mid-chest, behind the breastbone, or in the upper part of the abdomen. It is a sensation, not a condition.

GERD is what a clinician calls it when that event happens repeatedly enough to be a problem. The American College of Gastroenterology defines it as chronic symptoms or mucosal damage caused by the abnormal reflux of gastric contents into the esophagus and beyond.

One more way to hold it: reflux is what your body does, heartburn is what you feel, and GERD is what your chart says.

Heartburn Is a Symptom, Not a Condition

Heartburn gets treated like a diagnosis because there is an entire aisle of products named after it. But nobody has "heartburn" the way they have diabetes. They have an episode of it.

What it feels like is fairly specific: a burning that starts behind the breastbone and climbs toward the throat, usually within an hour of eating, often worse lying down or bending forward. It may come with a sour or bitter taste. It is not usually sharp, and it is not usually made worse by exertion, which is one clue (not a guarantee) that it is not cardiac.

The important nuance is that heartburn is an unreliable narrator. You can have significant reflux and never feel it, which is why silent reflux exists as a category at all. And you can feel intense burning with relatively little acid exposure if your esophagus is inflamed and sensitized.

Acid Reflux Is an Event, and Everyone Has It

This surprises people: reflux is normal. Healthy adults reflux after meals routinely and never notice. As the University of Utah puts it, most people experience minor acid reflux every once in a while, but repetitive reflux can lead to complications.

Reflux happens when the lower esophageal sphincter, the muscular ring at the base of the esophagus, weakens or relaxes when it should not. Most of those relaxations are your stomach venting gas, which is exactly what it is supposed to do. The problem is when acid rides along.

We went deep on the mechanics of that in What Is Acid Reflux? Causes, Symptoms, and How It Really Works, including why the valve opens, what pressure from below has to do with it, and where inflammation fits.

GERD Is a Diagnosis, Defined by Frequency and Damage

GERD is where reflux stops being physiology and starts being pathology. Two things move it across that line: how often symptoms occur, and whether tissue is being damaged.

On frequency, the sources are unusually consistent. MedlinePlus states that if you have symptoms two or more times a week, or if they cause damage to the lining of your esophagus, you may have GERD. The FDA uses the same threshold in its labeling, defining frequent heartburn as occurring 2 or more days a week. UC Davis Student Health puts it plainly: heartburn that occurs more than twice a week may be considered GERD.

Two or more times a week is the number worth remembering.

For scale, GERD affects roughly 10 to 20 percent of people in Western countries, with severe disease in about 6 percent, and the NIDDK estimates about 20 percent of people in the United States have it. This is not a rare condition.

Where Indigestion Fits (the Fourth Word)

Indigestion, known clinically as dyspepsia, is a broader umbrella: discomfort or fullness in the upper abdomen, often with bloating, early satiety, or nausea. It overlaps with reflux and frequently coexists with it, but it is centered on the stomach rather than the esophagus.

The rough distinction: if the discomfort burns and travels upward toward your throat, think reflux. If it sits heavy in your upper abdomen and feels like your meal is not moving, think indigestion. Plenty of people have both, and delayed gastric emptying can drive the two at once, which is one reason motility is worth taking seriously.

Two Kinds of GERD (and Why a Clean Endoscopy Does Not Clear You)

This is the part that trips up even well-informed patients. GERD splits into two forms: nonerosive reflux disease (NERD), where symptoms are present but the esophageal lining looks normal, and erosive reflux disease, where there are visible mucosal breaks.

And the split is lopsided. NERD accounts for 60 to 70 percent of patients, erosive esophagitis about 30 percent, and Barretts esophagus 6 to 12 percent. Only about 1 percent of the population has erosive esophagitis.

Translation: most people with GERD have a perfectly normal-looking esophagus. Being told "your scope was clean" is genuinely good news about tissue damage, and it is not the same as being told you do not have reflux disease. If you have been handed a clean report and still feel terrible, you are not imagining things.

There is also a demographic wrinkle worth knowing: NERD is more common in women, while reflux esophagitis is more common in men.

How Doctors Actually Tell the Difference

Mostly by listening. The NIDDK states that clinicians diagnose GER and GERD by reviewing your symptoms and medical history, and that testing is reserved for cases where symptoms suggest a complication or do not improve with treatment.

When testing is warranted, the common paths are:

• An empiric trial of acid suppression, typically eight weeks, when symptoms are typical and there are no alarm features. Response supports the diagnosis.

• Upper endoscopy, a flexible camera used to look for esophagitis, stricture, or Barretts, and to take tissue samples.

• Esophageal pH monitoring, which the NIDDK calls the most accurate way to detect stomach acid in the esophagus, done with a catheter or a wireless capsule.

When erosions are found, they are graded using the Los Angeles classification, an A through D system based on the length, location, and circumferential severity of the mucosal breaks.

When to Stop Self-Managing

Some symptoms move you past the antacid aisle regardless of frequency. Gastroenterologists call these alarm features: difficulty swallowing, painful swallowing, significant unexplained weight loss, gastrointestinal bleeding, or loss of appetite. The University of Utah adds bleeding, nausea, vomiting, and unexplained weight loss to its immediate-evaluation list.

There is also a quiet time limit on over the counter treatment that almost nobody reads. The FDA specifies that OTC proton pump inhibitors are intended for a 14-day course, usable up to three times per year. If you have been on one continuously for a year, you have quietly moved from self-care to unsupervised chronic therapy. That is a conversation worth having with your doctor, not a reason for alarm. Our overview of PPIs and traditional treatments covers the tradeoffs in more depth.

Why the Distinction Actually Matters

It matters because each label points to a different next step.

If you have occasional heartburn after a heavy meal, the answer is usually behavioral. Smaller portions, more time between dinner and bed, and identifying your specific triggers will do most of the work.

If you have frequent reflux crossing that two-times-a-week line, symptom relief alone stops being enough. Something structural is going on, whether that is a weakened sphincter, slow gastric emptying, elevated intra-abdominal pressure, or inflammation lowering your pain threshold. Suppressing acid will make it hurt less without changing why it is happening.

If you have GERD with damage, that belongs in a clinician's hands, and acid suppression may genuinely be necessary for a period of healing.

This is also where a lot of people get stuck. They read reflux as a pure acid problem, reach for the strongest acid blocker available, feel better for a while, and then find that stopping brings everything back. That is not a personal failure. It is what happens when a symptom tool gets asked to do a mechanism job. Our piece on acid balance explains why too little stomach acid can trigger the same symptoms as too much, which is the single most counterintuitive idea in this whole category.

It is also worth asking what is going on further downstream. Bacterial overgrowth in the small intestine produces gas, gas raises pressure, and pressure pushes upward. If your reflux comes bundled with bloating, Is Bacterial Overgrowth Causing Your Heartburn or GERD? is worth reading.

That mechanism-first thinking is the reason Re:flux exists in the form it does. Instead of shutting down acid production, it targets four drivers at once: lower esophageal sphincter function, gastric motility, acid balance, and inflammatory balance. You can see the reasoning laid out in The Acid Truth, or take the quiz to figure out which mechanism is most likely driving your symptoms.