Stomach acid is neutralized by alkaline compounds, most commonly mineral salts like calcium carbonate, magnesium hydroxide, and sodium bicarbonate. These are the active ingredients in over-the-counter antacids, and they work by chemically reacting with hydrochloric acid in your stomach to raise its pH. But antacids aren’t the only option. Your own saliva, plain water, and certain foods also help buffer acid, though to varying degrees.
How Antacids Neutralize Acid
Antacids contain alkaline mineral salts that react directly with the hydrochloric acid your stomach produces. The reaction converts the acid into water and a neutral salt, raising your stomach’s pH within minutes. This is a straightforward chemical reaction: a base meets an acid and cancels it out.
Not all antacid ingredients are equally powerful. Researchers measure an antacid’s strength using something called acid neutralizing capacity, which quantifies how much acid a given dose can counteract. Calcium carbonate (the ingredient in Tums) is the strongest common antacid salt, with a neutralizing capacity of 58 mEq per standard dose. Magnesium hydroxide (Milk of Magnesia) comes in at 35, aluminum hydroxide at 29, and sodium bicarbonate at 17. In practical terms, this means a calcium carbonate tablet neutralizes roughly three times as much acid as the same volume of baking soda.
The tradeoff for fast relief is short duration. Antacids typically keep stomach pH elevated for about 30 to 60 minutes when taken on an empty stomach, and somewhat longer when taken after a meal because food slows stomach emptying. If you need longer-lasting control, that requires a different approach entirely.
Baking Soda: The Kitchen Antacid
Sodium bicarbonate, or baking soda, is one of the oldest home remedies for heartburn. The standard dose for adults is half a teaspoon dissolved in a full glass of cold water, taken no more than every two hours. The daily maximum is five teaspoons, according to Mayo Clinic dosing guidelines.
It works, but it comes with important limits. Baking soda is extremely high in sodium, making it a poor choice if you have high blood pressure, heart disease, kidney problems, or are on a sodium-restricted diet. It can also interfere with other medications you take by mouth, so you should space it at least one to two hours away from other pills. And it’s not meant for ongoing use. If you’re reaching for baking soda regularly for more than two weeks, the underlying problem needs attention, not just the symptom.
Water Offers Brief Relief
Even a glass of plain water raises your stomach’s pH. A study measuring gastric pH in healthy volunteers found that water pushed stomach pH above 4 (a level where acid stops causing irritation) within one minute of drinking it. The catch: that effect lasted only about three minutes before acid levels returned to baseline. Antacids, by comparison, held pH above 4 for about 12 minutes in the same study. So water provides real but very temporary dilution, not true chemical neutralization.
Foods That Help Buffer Acid
Certain foods sit on the alkaline end of the pH scale and can help offset stomach acid, particularly in the context of acid reflux. Johns Hopkins Medicine identifies bananas, melons, cauliflower, fennel, and nuts as alkaline foods that may reduce reflux symptoms. These foods won’t neutralize acid the way an antacid tablet does, but they’re unlikely to trigger additional acid production, and their higher pH can gently buffer what’s already there.
Milk is a common home remedy that deserves a closer look. While it may feel soothing going down, research shows it actually stimulates more acid production. A study in both ulcer patients and healthy subjects found that 240 mL of milk (about one cup) significantly increased acid secretion, producing output equal to 20% to 35% of the stomach’s maximum capacity. This happens because milk contains both protein and calcium, both of which trigger acid release. So milk may briefly coat the stomach lining, but it makes the acid problem worse within the hour.
Your Body’s Built-In Neutralizer
Your saliva contains bicarbonate, the same alkaline compound found in baking soda, and it plays a surprisingly active role in protecting your esophagus from acid. Every time you swallow, saliva washes down into the esophagus and neutralizes any acid that has splashed up from the stomach. Research has shown that when acid reaches the upper esophagus, your salivary glands respond by tripling their bicarbonate output, jumping from about 28 to 87.5 microequivalents per minute. This appears to be a built-in defense mechanism against acid damage.
This is why chewing gum after meals can help with reflux. Chewing stimulates saliva production, which sends more bicarbonate into the esophagus. It won’t do much for acid sitting deep in the stomach, but for the burning sensation in your throat and chest, increased saliva flow provides measurable relief.
Neutralizing Acid vs. Stopping Its Production
Antacids neutralize acid that already exists in your stomach. They’re reactive, not preventive. Two other classes of medication work differently: they reduce how much acid your stomach makes in the first place.
H2 blockers (like famotidine, sold as Pepcid) block the chemical signal that tells your stomach lining to produce acid. They take longer to kick in than antacids but provide relief that lasts for hours instead of minutes. Proton pump inhibitors, or PPIs (like omeprazole, sold as Prilosec), suppress acid production even more aggressively and can be used for longer periods. As Cleveland Clinic notes, antacids work faster but wear off sooner, while H2 blockers and PPIs offer slower onset with more sustained control.
For occasional heartburn after a heavy meal, an antacid is the right tool. For symptoms that show up multiple times a week, reducing acid production is generally more effective than repeatedly neutralizing what’s already been made.
Risks of Over-Neutralizing
Stomach acid exists for a reason. It breaks down food, activates digestive enzymes, and kills bacteria. Neutralizing it occasionally is harmless, but chronic overuse of antacids, particularly calcium-based ones, can cause a serious condition called milk-alkali syndrome.
This syndrome involves dangerously high calcium levels in the blood, a shift in blood chemistry toward alkalosis, and acute kidney injury. It typically occurs in people consuming more than 4 grams of calcium daily through supplements or antacids, though cases have been reported with as little as 1 gram per day. Older adults are at higher risk because their bones are less able to absorb excess calcium. Certain medications, including thiazide diuretics and common anti-inflammatory drugs, can compound the problem by reducing the kidneys’ ability to flush calcium out.
Without treatment, milk-alkali syndrome can progress to permanent kidney damage and calcium deposits in organs throughout the body, including the lungs, liver, and brain. Neurological symptoms like confusion and even seizures have been reported when calcium levels climb high enough. This is rare with occasional antacid use, but it’s the reason the label on your Tums bottle includes a daily maximum you shouldn’t ignore.