What does stomach acid actually do?

That burning feeling in your chest after a big meal? That's your stomach doing its job. The stomach runs at a pH between 1.5 and 3.5 — about as acidic as battery acid — and it needs to be that way to break down the proteins in your food through enzymatic digestion.

Stomach acid also activates pepsin, the enzyme that actually cuts proteins into smaller pieces your body can use. Without that acid environment, pepsin never gets switched on. That same acidity signals your small intestine to call in backup — hormones that tell the pancreas to release its own digestive enzymes.