Your stomach manufactures a new lining every three days to avoid digesting itself.
As a part of the digestive process, your stomach secretes hydrochloric acid (HA). HA is a powerful corrosive compound also used to treat various metals. The HA your stomach secretes is also powerful, but mucous lining the stomach wall keeps it within the digestive system. As a result, it breaks down the food you consume, but not your own stomach.