Stomach (or gastric) acid is a mixture of hydrochloric acid, potassium chloride and sodium chloride. An acid’s strength is measured on the pH scale. The range of acid strength goes from 0(strongest) to 6(weakest). Stomach acid measures between 1 and 3 on this scale, making it quite a strong acid.
The reason the acid doesn’t burn our insides is because the stomach produces mucus to line itself and protect it from the acid. We need acid in our stomachs as this starts the process of breaking our food down(digestion), so it can be absorbed by our bodies.
After the food leaves the stomach and enters the next part of your digestive system, the pancreas releases a bicarbonate which helps to neutralise, or weaken, the acid so it doesn’t damage your insides.
For further reading and facts on the stomach, click on this link.
For a video that explains the part of the stomach in the digestive system, please see below: