How does HCl not burn our stomach? How does the digestive acid (HCl) not burn the surrounding membrane of our stomach? It digests the majority of raw food we eat but how does it stay safely in our stomach? Also, how does the stomach maintain the ability for a human body to retain HCl for all lifetime?

Mucous-producing cells at the neck of the gastric pits create a layer of protective mucous covering the stomach lining. This mucous layer includes bicarbonate ions which act as a chemical barrier against the protons in gastric juice. See here for some evidence.

The stomach lining stays protected because the mucous layer is continuously replenished.