What Is Acid Reflux, Exactly?

Acid reflux, known clinically as gastroesophageal reflux (GER), is what happens when stomach contents come back up into your esophagus. That's the whole definition. It's a directional problem, not simply an acid problem.

Here's how digestion is supposed to work.

Your esophagus is a muscular tube about ten inches long that carries food from your throat to your stomach. At the bottom sits the lower esophageal sphincter (LES), a ring of smooth muscle that stays closed most of the time and opens when you swallow. Wrapped around it is the crural diaphragm, which functions as a second, external sphincter.

I tell my patients to think of the LES as the lid on a pot.

When the lid stays closed, stomach contents stay where they belong.

When it doesn't close properly—or pressure builds inside the stomach—stomach contents can move upward into the esophagus.

Your stomach is built to handle acid. Your esophagus isn't. That's why reflux feels like burning.

Here's something many people don't realize: reflux itself is normal. Healthy people reflux after meals and never notice it. The clinical line gets crossed when the frequency, duration, or consequences change.

For a plain-language primer on the vocabulary, our gut health glossary is a useful bookmark.

Acid Reflux vs. GERD: Where the Line Sits

People often use these terms interchangeably, but they're not the same thing.

Acid reflux (GER) is the event: stomach contents moving backward into the esophagus.

GERD is the disease: reflux that causes repeated, bothersome symptoms or leads to complications over time.

Heartburn is one symptom reflux can produce. Not everyone with GERD experiences heartburn, and not everyone with heartburn has GERD.

The rough working threshold clinicians use is frequency. The National Library of Medicine puts it at symptoms occurring two or more times a week, which lines up with FDA labeling for over-the-counter reflux medications.

How Acid Reflux Actually Works: Four Mechanisms

This is where things get interesting.

One of the biggest misconceptions about reflux is that there's a single cause.

There isn't.

In most people, reflux develops because several digestive functions are no longer working together the way they're supposed to.

When I think about reflux, I'm usually thinking about four different mechanisms.

1. The LES loses tone, or opens at the wrong moment

At rest, your LES maintains a resting pressure of roughly 30 mmHg, with a normal range between 15 and 30 mmHg. When you swallow, that pressure briefly drops to about 3 mmHg—roughly matching the pressure inside your stomach—so food can pass through. Then it closes again.

The problem is a separate phenomenon called a transient lower esophageal sphincter relaxation, or TLESR.

These spontaneous openings last between 10 and 45 seconds, considerably longer than a swallow, and they aren't triggered by swallowing at all. They're a normal way for your stomach to vent gas.

In fact, TLESRs account for 94 percent of reflux episodes in healthy people and about 65 percent in people with reflux disease.

Here's the finding that changes how we think about reflux.

Research published in Frontline Gastroenterology found that people with reflux disease don't actually have more TLESRs than healthy volunteers.

What changes is what comes through the opening.

In healthy people, these relaxations mostly release gas.

In people with GERD, they often allow stomach contents to move upward.

So the question isn't just, "Why is the valve opening?"

It's also, "Why is stomach contents sitting there, ready to move upward when it does?"

Several everyday factors also reduce LES pressure, including fatty foods, chocolate, smoking, and alcohol. That's the science behind many of the classic trigger foods people hear about.

2. Pressure Builds from Below

The LES isn't the only part of the equation.

The pressure inside your stomach matters just as much.

Think of your stomach like a bottle of sparkling water.

If it empties on schedule, pressure stays manageable.

If food sits there longer than it should, pressure builds. And when pressure builds, it has to go somewhere. The easiest direction is up.

That's why gastric motility—how efficiently your stomach empties—is such an important part of the reflux conversation.

Under normal circumstances, your stomach contracts in a coordinated rhythm of about three contractions per minute. According to the University of North Carolina Center for Functional GI and Motility Disorders, it generally takes 90 to 120 minutes for the first part of a meal to reach the large intestine, with the final portion taking up to five hours.

When that rhythm slows, reflux becomes more likely.

Delayed gastric emptying is found in approximately 10 to 15 percent of patients with reflux.

The esophagus also has an important job after reflux occurs.

Every time stomach contents move upward, the esophagus relies on coordinated muscle contractions—called peristalsis—to push everything back where it belongs.

When that clearing mechanism isn't working well, stomach contents stay in contact with the esophagus longer.

The same review found impaired esophageal clearance in 25 percent of patients with mild esophagitis and nearly half of patients with severe esophagitis.

This is one reason I often talk about motility, not just acid.

It's also why eating late at night can be such a problem. If your stomach hasn't finished emptying before you lie down, you've increased both the pressure inside the stomach and the opportunity for reflux to occur.

3. The Diaphragm and the Hiatal Hernia Factor

Most people have heard of a hiatal hernia.

Fewer people understand why it matters.

Remember that the LES isn't working alone.

Your crural diaphragm wraps around the LES and acts like an additional layer of support, especially when you take a breath or when pressure inside your abdomen increases.

Together, these two structures help keep stomach contents where they belong.

A hiatal hernia develops when part of the stomach slides upward through the opening in the diaphragm.

When that happens, the LES and the diaphragm are no longer working together as effectively.

The numbers are striking.

Between 50 and 94 percent of patients with GERD have a sliding hiatal hernia, and research shows that transient LES relaxations become more common as the hernia becomes larger.

But here's something that often surprises people.

Having a hiatal hernia does not automatically mean you'll have reflux.

Roughly 55 to 60 percent of people over the age of 50 have a hiatal hernia, yet only about 10 percent ever develop symptoms.

That's an important distinction.

A hiatal hernia increases risk, but it's only one piece of the puzzle.

Acquired hiatal hernias are associated with conditions that repeatedly increase pressure inside the abdomen, including obesity, pregnancy, chronic constipation, and chronic coughing.

Notice the common theme.

They're all pressure problems.

4. Inflammation Lowers the Threshold

This is probably the least discussed mechanism, but it's an important one.

An inflamed esophagus becomes a more sensitive esophagus.

Once the lining is irritated, even a normal amount of acid exposure can produce more discomfort than it otherwise would.

Inflammation can also interfere with the coordinated muscle contractions that normally help clear refluxed material from the esophagus.

That creates a cycle.

Reflux leads to inflammation.

Inflammation makes the tissue more sensitive and reduces normal clearance.

Reduced clearance allows reflux to remain in contact with the esophagus longer.

And the cycle continues.

Breaking that cycle often means addressing the inflammation itself—not simply trying to neutralize whatever is causing the irritation.

We cover this in more detail in Inflammation: The Silent Driver That Makes Reflux Feel Worse.

These four mechanisms—LES function, gastric motility, pressure, and inflammation—are the framework I use when thinking about reflux.

They're also the foundation of Why Reflux Happens and Why Re:flux Works on Four Core Mechanisms.

What Acid Reflux Feels Like

When most people think about acid reflux, they think about heartburn.

The FDA describes heartburn as an uncomfortable burning feeling in the chest, behind the breastbone, or in the upper abdomen.

That's certainly the most recognizable symptom.

But it's far from the only one.

People with reflux may also experience:

• Regurgitation, where a sour or bitter taste rises into the throat or mouth.

• Chest pain, which can sometimes mimic heart-related chest pain and should always be medically evaluated the first time it occurs.

• A chronic cough, hoarseness, or laryngitis that doesn't seem related to a cold.

• Difficulty swallowing or the sensation that something is stuck in the throat.

• Worsening asthma symptoms.

• Tooth enamel erosion, which is sometimes first noticed by a dentist.

That last group of symptoms is often referred to as extraesophageal reflux.

The University of Iowa Head and Neck Protocols include chronic cough, hoarseness, dysphonia, asthma, dental erosion, sinus disease, postnasal drip, and throat clearing among its presentations.

If you've been chasing a chronic cough or throat symptoms without finding an answer, reflux may not be the first thing that comes to mind—but it should certainly be part of the conversation.

And here's one more point that's worth remembering.

The National Institute of Diabetes and Digestive and Kidney Diseases is very clear that not everyone with GERD experiences heartburn or regurgitation.

That's one reason reflux can be so easily overlooked.

What Causes Acid Reflux? The Risk Factors That Hold Up

When patients ask me, "What causes acid reflux?" they're often expecting a single answer.

The reality is that reflux usually develops because several factors come together.

The National Institute of Diabetes and Digestive and Kidney Diseases groups the strongest risk factors around one common theme: anything that weakens the lower esophageal sphincter or increases pressure against it.

Excess Weight

This is one of the strongest and most consistent risk factors we know.

People with obesity experience about two-thirds more transient LES relaxations per hour than people who are not obese. More relaxations create more opportunities for stomach contents to move upward.

Pregnancy

Pregnancy affects reflux in two ways.

Hormonal changes relax smooth muscle throughout the body, including the LES. At the same time, the growing uterus increases pressure within the abdomen.

Those two factors together make reflux much more common during pregnancy.

Smoking

Nicotine directly reduces LES pressure, making it easier for stomach contents to reflux into the esophagus.

That includes secondhand smoke as well.

Certain Medications

Some medications can contribute to reflux by relaxing the LES or slowing normal digestive function.

The NIDDK specifically identifies:

• Benzodiazepines

• Calcium channel blockers

• Some asthma medications

• NSAIDs

• Tricyclic antidepressants

If your reflux began after starting a new medication, it's worth discussing with your healthcare provider before making any changes.

Hiatal Hernia

As we discussed earlier, a hiatal hernia doesn't automatically cause reflux.

But it does increase the likelihood by disrupting the normal relationship between the LES and the diaphragm.

Trigger Foods

Certain foods have been shown to reduce LES pressure or increase reflux symptoms.

UC Davis includes:

• Alcohol

• Peppermint

• Chocolate

• Caffeine

• Citrus

• Fried foods

• Fatty foods

• Garlic

• Onions

• Tomato-based products

One point I always make to patients is that trigger foods are highly individual.

Fat and chocolate have measurable effects on LES pressure.

Whether tomatoes or coffee are triggers for you is something only your own experience can answer.

Keeping a food and symptom diary is often much more useful than eliminating a long list of foods you may tolerate perfectly well.

Our article on why even "healthy" foods sometimes backfire explores this in more detail.

The Gut Microbiome Connection Most Articles Skip

This is where the conversation starts getting really interesting.

For years, reflux has been viewed almost entirely as an upper digestive tract problem.

But digestion doesn't happen in isolated compartments.

Everything is connected.

One area receiving increasing attention is the relationship between small intestinal bacterial overgrowth (SIBO) and reflux.

SIBO is defined as an excessive concentration of bacteria within the small intestine. In clinical practice it's most commonly evaluated using breath testing, where a rise in hydrogen of more than 20 parts per million within 90 minutes—or methane above 10 parts per million—is considered positive.

So why might SIBO matter?

Think back to pressure.

Bacteria ferment carbohydrates.

Fermentation produces gas.

Gas increases pressure inside the small intestine and stomach.

And increased pressure pushes upward against a lower esophageal sphincter that may already be underperforming.

That's the proposed mechanical connection.

A 2025 case-control study published in BMC Gastroenterology explored exactly this question.

Among 103 participants, SIBO was present in 64 percent of patients with GERD compared with 43.4 percent of healthy controls.

Hydrogen-producing SIBO was also significantly more common in the GERD group.

Now let's be careful not to overinterpret those findings.

This was a relatively small study.

It shows an association—not proof that SIBO causes reflux.

We still don't know which condition develops first, and SIBO certainly isn't the explanation for everyone with reflux.

But it does suggest there's more happening than stomach acid alone.

There's another interesting piece to this story.

The same NIH review notes that SIBO is associated with achlorhydria, or very low stomach acid, and specifically identifies proton pump inhibitors as one potential cause.

Why does that matter?

Because stomach acid is one of the body's natural defenses against bacterial overgrowth.

Reduce acid for long enough, and that protective barrier changes.

Whether that consistently leads to SIBO remains an area of active research, but it's an important question—and one worth continuing to study.

If this sounds familiar, our articles Is Bacterial Overgrowth Causing Your Heartburn or GERD? and Dysbiosis: When Your Gut Microbes Start Running the Show explore the topic in greater detail.

How Long Does Acid Reflux Last?

An occasional episode of reflux may last anywhere from a few minutes to a couple of hours.

Most people can relate to that experience after a large meal, lying down too soon after eating, or bending over.

Those occasional episodes aren't usually cause for concern.

GERD is different.

GERD is defined by persistence.

Without addressing the underlying factors contributing to reflux, symptoms often continue.

This is one reason many people find themselves caught in a frustrating cycle.

Acid suppression may reduce symptoms while they're taking the medication.

But if the underlying mechanics haven't changed, symptoms often return once treatment stops.

That's why I think it's important to ask not only how to reduce symptoms, but also why reflux is happening in the first place.

When Acid Reflux Becomes Something to Take Seriously

Most reflux is uncomfortable rather than dangerous.

But chronic, untreated reflux can lead to complications including:

• Esophagitis

• Esophageal strictures

• Barrett's esophagus

Barrett's esophagus affects approximately 5 percent of adults in the United States and carries a small increase in the risk of esophageal cancer.

Certain symptoms deserve prompt medical evaluation.

These include:

• Difficulty swallowing

• Pain with swallowing

• Unexplained weight loss

• Gastrointestinal bleeding

• Loss of appetite

New or severe chest pain—especially if accompanied by shortness of breath—should always be evaluated immediately to rule out a heart-related cause.

One additional point worth mentioning involves over-the-counter proton pump inhibitors.

The FDA recommends using OTC PPIs for 14-day courses, up to three times per year.

If you've been taking one continuously for months or years without reviewing your treatment plan with your healthcare provider, it's worth having that conversation.

We've written more about this in Why PPI Rebound Is Real and our overview of PPIs and Traditional Reflux Treatments.

This isn't about being anti-medication.

PPIs are valuable medications and, for many people with erosive disease, they're an important part of treatment.

But reducing acid doesn't necessarily change the underlying reason reflux is happening.

A Mechanism-First Way to Think About Reflux

If there's one idea I'd like you to take away from this article, it's this:

Reflux isn't simply an acid problem. It's a digestive function problem.

Acid is what you feel.

The real question is why stomach contents are moving into the esophagus in the first place.

That's why I approach reflux differently.

Instead of asking one question—"How do we reduce acid?"—I ask four.

• Is the lower esophageal sphincter doing its job?

• Is the stomach emptying the way it should?

• Is stomach acid where it belongs, doing the job it was designed to do?

• Is inflammation making a normal amount of reflux feel much worse?

When you start asking those questions, reflux begins to make a lot more sense.

It also changes how you think about treatment.

We explore the acid question in more detail in The Acid Truth, because one of the biggest misconceptions in digestive health is that all reflux comes from producing too much stomach acid.

Sometimes the issue isn't how much acid your stomach makes.

It's where that acid ends up.

Where Re:flux Fits

Those four mechanisms are exactly why we developed Re:flux.

As both a gastroenterologist and someone who lived with reflux myself for more than 30 years, I kept coming back to the same question.

Why are we only talking about acid?

Acid is an essential part of digestion.

The goal isn't to eliminate it.

The goal is to help keep stomach contents where they belong.

Rather than focusing on acid suppression alone, Re:flux was formulated to support four important aspects of upper digestive physiology.

• Hesperidin, a citrus bioflavonoid that supports healthy lower esophageal sphincter function and digestive tissue integrity.

• Dandelion root, traditionally used to support bile flow and healthy digestion.

• Noni fruit, which provides naturally occurring plant compounds that support digestive balance and a healthy inflammatory response.

• Atractylodes macrocephala, traditionally used to support healthy gastric motility and digestive rhythm.

Each ingredient was selected because reflux involves more than a single pathway.

It involves how well your stomach empties, how effectively the LES functions, the balance of your digestive environment, and the health of the tissues exposed to reflux.

You can learn more about the science behind this approach in The Acid Truth or explore each ingredient in our Re:flux Ingredient Guide.

Not sure which mechanism may be contributing to your symptoms?

Take our reflux quiz.

It takes about two minutes and can help you better understand where to start.