The human stomach secretes a very acidic gastric juice to help in breaking down ingested food. The gastric juice contains hydrochloric acid with a pH of 1.5-3.5
The strength of acids is usually measured by using the pH scale, that is the measure of the concentration of hydrogen ions present in the acid. The scale is from 1-14. The lower the pH, the more acidic a substance is.
The acid in the stomach is very potent. In fact, an in vitro study showed that the acid in the human stomach is powerful enough to dissolve razor blades. Hence, the stomach produces a layer of thick mucus that helps to protect its walls from being digested by the acid it secretes.