Biology
How does your stomach avoid digesting itself?
Quick fact
Stomach acid (hydrochloric acid) has a pH as low as 1.5, but the stomach lining secretes a thick bicarbonate-rich mucus that protects the tissue from digestion.
Why this is interesting
Your stomach produces acid powerful enough to eat through steel, yet it doesn't consume itself—thanks to a microscopic layer of mucus that's constantly being rebuilt.
Read the full explanation
Understanding How does your stomach avoid digesting itself?
The mucus forms a physical barrier, and bicarbonate ions neutralize any acid that penetrates, keeping the pH near the stomach wall at a safe 7.0—neutral.
A deeper explanation
This protection is a high-turnover system: the stomach lining replaces itself completely every 3-4 days to repair any microscopic acid damage. Peptic ulcers occur when this balance fails—often due to bacteria (H. pylori) that weaken the mucus layer, or NSAID drugs that reduce mucus production. The stomach is essentially a self-sacrificing organ: it's okay with a little self-digestion, as long as it regenerates fast enough. This biological 'acid warfare' is a marvel of evolutionary engineering, allowing us to break down proteins while keeping our own tissue intact—a perfect example of controlled danger inside our own bodies.