“Hydrolic acid” is a common misspelling of hydrochloric acid, a strong acid with the chemical formula HCl. It’s one of the most widely produced chemicals in the world, used in everything from steel manufacturing to food processing. It also happens to be the acid your stomach produces naturally to digest food.
Hydrochloric acid is a solution of hydrogen chloride gas dissolved in water. In concentrated form, it’s a colorless to slightly yellow liquid that fumes in open air and can cause severe burns on contact. You may also see it sold under the name “muriatic acid,” which is simply an older term for the same chemical, typically at a slightly lower concentration for commercial and household use.
How Your Body Uses Hydrochloric Acid
Your stomach lining contains specialized cells called parietal cells that produce hydrochloric acid continuously. In a healthy person, the pH of stomach fluid sits between 1.0 and 2.5 on an empty stomach, making it acidic enough to dissolve small bones and kill most bacteria that ride in on your food. After a meal, the pH rises to somewhere between 3 and 7 depending on what and how much you ate.
This acid does more than just break food into smaller pieces. It activates a key digestive enzyme by converting an inactive substance called pepsinogen into pepsin, which is what actually breaks down the proteins in your food. That conversion only happens when the pH falls between 1.0 and 3.0, so if your stomach acid is too weak, protein digestion suffers. The acid also creates a hostile environment for harmful bacteria, acting as a first line of defense before food moves deeper into your digestive system.
Major Industrial Uses
Steel pickling is the single largest consumer of hydrochloric acid, accounting for roughly 40% of all HCl produced globally. When steel is hot-rolled during manufacturing, a layer of iron oxide (rust) forms on the surface. To remove it, steel passes through baths of 15 to 20% hydrochloric acid heated to 60 to 80°C for anywhere from 2 to 10 minutes, depending on how thick the rust layer is. The result is a clean, smooth surface ready for coating or further processing.
In the oil and gas industry, 15% hydrochloric acid is pumped into wells to dissolve carbonate rock formations underground, opening pathways for oil and gas to flow more freely. Rare earth processing also relies on HCl to dissolve rare earth oxides so the metals can be extracted and purified.
Food production uses food-grade hydrochloric acid (at concentrations between 3 and 30%) for several purposes. Corn syrup manufacturing is one of the biggest: the acid breaks the bonds between glucose units in corn starch, converting it into liquid glucose. HCl also helps regulate pH during gelatin and citric acid production.
Other notable uses include PVC plastic manufacturing, where HCl serves as a direct raw ingredient, and pharmaceutical production, where it’s used to create hydrochloride salt versions of drugs that dissolve more easily in the body. Water treatment plants use it to adjust pH and regenerate filtration systems.
Muriatic Acid Is the Same Thing
If you’ve seen jugs of muriatic acid at a hardware store, that’s hydrochloric acid under its older commercial name. The concentration is typically lower than laboratory-grade HCl, and it sometimes has a yellowish tint from trace amounts of iron picked up during manufacturing. Standard muriatic acid is roughly 10 molar (about 31% concentration), though “green” or reduced-fume versions sold for home use are closer to 6 molar. People commonly use it to clean concrete, etch surfaces before painting, and lower the pH in swimming pools.
Health Hazards of Exposure
Hydrochloric acid is safe inside your stomach, which has a protective mucus lining. Outside the body, it’s a different story. The risks depend on whether you’re dealing with the liquid acid, the gas (hydrogen chloride), or just dilute mist.
Skin and Eyes
Concentrated hydrochloric acid causes deep chemical burns on contact and can leave disfiguring scars. Even dilute solutions or vapor exposure can redden and inflame the skin. Eye exposure is particularly dangerous: concentrated vapor or liquid can destroy corneal cells and lead to cataracts or glaucoma, while even dilute contact causes stinging pain and surface ulcers.
Breathing It In
Hydrogen chloride gas is intensely irritating to the nose, throat, and airways. Brief exposure at just 35 parts per million causes throat irritation, and concentrations of 50 to 100 ppm are barely tolerable for an hour. At high concentrations, the throat can swell and spasm rapidly enough to cause suffocation. Severe exposure may lead to fluid accumulation in the lungs or trigger a condition called Reactive Airway Dysfunction Syndrome, a form of chemically induced asthma that can persist long after the exposure ends.
The U.S. workplace ceiling limit set by OSHA is 5 ppm, meaning air concentrations should never exceed that level at any point during a work shift.
Handling It Safely at Home
If you’re using muriatic acid for pool maintenance, concrete cleaning, or similar projects, always work outdoors or in a well-ventilated area. Chemical-resistant gloves, splash-proof goggles, and a respirator rated for acid gases are the minimum protective gear. Always add acid to water rather than water to acid, since the reverse can cause a violent splash of hot, concentrated solution. Keep a supply of baking soda nearby to neutralize small spills, and store the container tightly sealed in a cool, dry area away from metals, which it will corrode.