Which acid is the main component of the stomach's digestive juices?

Hydrochloric acid is the main acid component of the stomach’s digestive juices. It is produced by parietal cells in the stomach lining and gives gastric juice its strongly acidic character.

In humans, stomach acid typically has a pH between 1 and 3. This acidity helps unfold proteins and activates pepsinogen, an inactive enzyme made by chief cells, into pepsin, which begins breaking proteins into smaller fragments. The acid also helps destroy many microorganisms swallowed with food.

A common mix-up is to call the entire digestive secretion “hydrochloric acid.” Gastric juice is a mixture that includes hydrochloric acid, enzymes such as pepsin, mucus, water, and other substances. The stomach protects itself with a mucus-and-bicarbonate barrier, while bicarbonate from the pancreas later neutralizes the acid in the duodenum.

The acid is secreted through microscopic canaliculi in parietal cells by H+/K+ ATPase proton pumps. A typical adult stomach can produce roughly 1.5 liters of gastric juice per day.