Low stomach acid, known medically as hypochlorhydria, happens when your stomach doesn’t produce enough hydrochloric acid to properly break down food. The causes range from common infections and medications to autoimmune conditions and the natural effects of aging. Understanding why acid production drops can help you figure out what’s going on and what to do about it.
How Your Stomach Makes Acid
Your stomach lining contains specialized cells called parietal cells, and their sole job is producing hydrochloric acid. These cells don’t just pump acid constantly. They respond to a web of signals: the vagus nerve (which connects your brain to your gut), hormones like gastrin and histamine, and even the physical act of seeing or smelling food. When any part of this signaling system breaks down, acid production can drop.
This matters because stomach acid does more than digest protein. It kills bacteria in your food, triggers the release of digestive enzymes further down the tract, and helps you absorb key nutrients like iron, calcium, and vitamin B12. When acid levels fall too low, the ripple effects go well beyond the stomach itself.
H. pylori Infection
One of the most common causes of low stomach acid worldwide is infection with a bacterium called H. pylori. About half the global population carries it, though not everyone develops symptoms. When the infection takes hold in the main body of the stomach (the corpus), it triggers chronic inflammation that directly suppresses acid output in two ways.
First, the bacterium produces substances that inhibit parietal cells from doing their job. Second, the infection ramps up production of an inflammatory molecule called interleukin-1β, which blocks both the acid-producing cells and the nearby cells that release histamine, one of the key signals telling your stomach to make acid. Over time, persistent H. pylori infection can cause gastric atrophy, meaning the acid-producing cells are permanently lost, not just temporarily suppressed. This is why long-standing infections sometimes lead to irreversible drops in acid production.
Long-Term Acid-Suppressing Medications
Proton pump inhibitors (PPIs) are among the most widely prescribed drugs in the world. Brand names like omeprazole, lansoprazole, and esomeprazole are familiar to millions of people who take them for heartburn or acid reflux. These drugs work by directly blocking the acid pumps inside parietal cells, and they’re very effective at it.
Short-term use typically isn’t a concern, but long-term PPI therapy can push the stomach into a state of sustained low acid. In some cases, prolonged use leads to near-complete absence of acid production, a condition called achlorhydria. This effect is more pronounced with PPIs than with milder acid-suppressing options like H2 blockers or antacids, which reduce acid without shutting it down as aggressively. If you’ve been on a PPI for months or years, your stomach pH is likely significantly higher (meaning less acidic) than it would be naturally.
One complication of stopping PPIs after long-term use is rebound acid hypersecretion, where your stomach temporarily overproduces acid once the drug is removed. This can make it feel like you need the medication even more, creating a cycle that’s hard to break without tapering gradually.
Autoimmune Atrophic Gastritis
In autoimmune atrophic gastritis, the immune system mistakenly identifies parietal cells as foreign and attacks them. This inherited condition produces antibodies against both the parietal cells and the proton pump machinery they use to secrete acid. The result is a slow, progressive destruction of your stomach’s ability to make acid at all.
Because parietal cells also produce intrinsic factor, a protein essential for absorbing vitamin B12, people with this condition often develop B12 deficiency and eventually pernicious anemia. The loss of acid also triggers a feedback loop: the stomach senses that acid levels are too low and floods the system with the hormone gastrin to try to stimulate more production. Gastrin levels can climb to extremely high levels, sometimes exceeding 1,000 pg/mL, which is far above normal.
Diagnosis usually involves an endoscopic biopsy to examine the stomach lining directly. Doctors may also check for antibodies against parietal cells and intrinsic factor in your blood, though these tests aren’t always ordered unless the biopsy raises suspicion. Autoimmune atrophic gastritis is less common than H. pylori or medication-related causes, but it’s important to catch because of its association with B12 deficiency and a small but real increase in the risk of certain stomach tumors over time.
Aging and Nutrient Deficiencies
Stomach acid production naturally declines with age. Estimates suggest that a significant portion of adults over 60 have some degree of reduced acid output. This happens partly because the stomach lining gradually thins over decades, reducing the total number of functioning parietal cells. It’s not a disease process in most cases, just a slow erosion of capacity.
Zinc deficiency can also contribute to low stomach acid, since zinc is needed for the enzymatic processes involved in acid production. Similarly, chronic stress may play a role by altering vagus nerve signaling, though this connection is less well established than infection or medication-related causes. Poor nutrition and restrictive diets that limit protein can reduce the stimulus for acid secretion, since protein in the stomach is one of the triggers for gastrin release.
Symptoms That Suggest Low Acid
Low stomach acid doesn’t always produce obvious symptoms, which is part of why it often goes unnoticed. When symptoms do appear, they can look a lot like the opposite problem, excess acid. Bloating, gas, and a feeling of uncomfortable fullness after meals are common because food sits in the stomach longer without adequate acid to break it down. Undigested food can ferment, producing gas that gets mistaken for acid reflux.
Other signs include frequent belching after meals, nausea, and loose stools or diarrhea, since poorly digested food can irritate the intestines. Over time, nutrient malabsorption becomes a bigger issue. Iron deficiency, B12 deficiency, and low calcium levels can all develop, sometimes causing fatigue, brittle nails, hair thinning, or neurological symptoms like tingling in the hands and feet.
How Low Stomach Acid Is Tested
The gold standard for measuring stomach acid is a test called gastric pH monitoring, where a small probe is placed in the stomach to measure acidity directly. In practice, this isn’t commonly done outside of research settings. Doctors more often look at indirect markers: high fasting gastrin levels, low B12, low iron despite adequate dietary intake, and biopsy findings showing thinning of the stomach lining.
You may have encountered the “baking soda test” online, where you drink a mixture of baking soda and water on an empty stomach and time how long it takes to burp. The idea is that the sodium bicarbonate reacts with stomach acid to produce carbon dioxide gas. In reality, this test has no clinical evidence supporting its accuracy. Most burping after drinking the mixture comes from swallowed air, not a chemical reaction with stomach acid, making false positives and false negatives equally likely. It’s not a reliable way to assess your acid levels.
What Helps Restore Acid Levels
Treatment depends entirely on the underlying cause. If H. pylori is responsible, eradicating the infection with a course of antibiotics often allows the stomach lining to recover and acid production to improve, though this depends on how much atrophy has already occurred. If PPIs are the culprit, working with your doctor to taper the dose gradually rather than stopping abruptly can help your stomach recalibrate.
For autoimmune atrophic gastritis, the damage to parietal cells is generally permanent. Management focuses on replacing what’s lost: B12 injections, iron supplementation, and regular monitoring for complications. Some people with low stomach acid from various causes find that taking betaine hydrochloride supplements with meals helps improve digestion, though this should be approached carefully and isn’t appropriate for everyone, particularly anyone with ulcers or erosive gastritis.
Addressing nutritional gaps, particularly zinc and B vitamins, can support whatever acid-producing capacity remains. Eating protein-rich meals, chewing thoroughly, and avoiding drinking large volumes of liquid during meals are simple habits that may help optimize the acid your stomach does produce.