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Your stomach acid could dissolve a razor blade — so why doesn't it eat your stomach?
💡 Your stomach survives its own acid not by being acid-proof, but by coating itself in a bicarbonate-rich mucus layer and replacing its lining every few days.
The acid inside your stomach is genuinely ferocious. It's mostly hydrochloric acid, sitting around a pH of 1.5 to 3.5 — acidic enough to corrode metal and strong enough to break down the tough proteins in a steak. Its job is to unravel food, kill swallowed bacteria, and switch on digestive enzymes. So the obvious question is: why doesn't it simply digest the stomach itself, which is also made of protein?
The answer is a living, self-renewing shield. Special cells in the stomach wall secrete a thick layer of mucus laced with bicarbonate, a base that neutralizes acid right at the surface. This creates a gradient: brutally acidic in the open cavity, but nearly neutral against the actual cell lining. The barrier is your body's version of a fireproof suit.
Even better, the stomach doesn't rely on the suit lasting forever. Its lining is one of the fastest-regenerating tissues in the body, replacing its surface cells roughly every few days. When acid or irritants like alcohol and certain painkillers overwhelm the mucus barrier, the exposed tissue can be damaged — that's how many ulcers form, often with help from the bacterium H. pylori.
So you're not protected because the acid is weak. You're protected because your body out-races it, rebuilding the wall faster than the acid can wear it down.