Your gut acid can melt steel

The hydrochloric acid in your stomach is potent enough to dissolve a metal zinc nail. The only reason it doesn't melt your own chest is a sacrificial layer of alkaline mucus that coats your stomach lining.

This mucus is rich in bicarbonate, which neutralizes the acid on contact. It acts as a neutral zone where the burning liquid meets a cooling base.

Even with this shield, the environment is so corrosive that your stomach must sprout a completely new lining every three to four days. You are effectively growing a new stomach twice a week to stay ahead of your own digestion.

If the mucus production slows down for even a few hours, the acid begins to eat the living tissue underneath. This failure of the shield is exactly what causes a peptic ulcer, meaning your body has quite literally started to digest itself.