Stomach acid, primarily composed of hydrochloric acid, is a digestive fluid produced by the cells lining the stomach. Its main function is to break down food, particularly proteins, and to create an acidic environment that helps kill harmful bacteria. This process is essential for proper digestion and nutrient absorption. The acidity of stomach acid is measured on the pH scale, typically ranging from 1.5 to 3.5. This strong acidity not only aids in digestion but also activates enzymes like pepsin, which further assist in breaking down food. The stomach's lining is protected from this acid by a thick layer of mucus.