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The acid in your stomach is strong enough to digest food — and would eat through the stomach wall itself if nothing protected it.
Your stomach lining regenerates every few days, a rapid renewal necessary because the strong acid your stomach produces to help digest food would otherwise begin to damage the stomach's own tissue over time. To prevent this, the cells lining the stomach wall are constantly shed and replaced, along with a protective layer of mucus, keeping the barrier fresh enough to withstand the corrosive environment inside.
A renewal cycle measured in years, or the idea that the lining never regenerates at all, would leave the stomach dangerously vulnerable to its own acid, since ongoing exposure to gastric acid demands a much faster turnover than either slower timeframe would allow.
When this protective renewal process breaks down, for instance due to certain bacterial infections or long-term irritation, it can lead to conditions like gastric ulcers, where the stomach's own acid manages to damage the wall it is normally kept safely away from.
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