Hydrochloric acid (HCl) secretion assists protein digestion by activating pepsinogen to pepsin, renders the stomach sterile against orally-ingested pathogens, prevents bacterial or fungal overgrowth of the small intestine, encourages the flow of bile and pancreatic enzymes, and facilitates the absorption of a variety of nutrients, including folic acid, ascorbic acid, beta-carotene, non-heme iron, and some forms of calcium, magnesium, and zinc. Numerous studies have shown acid secretion declines with advancing age and impaired HCl production and secretion is seen in a variety of clinical conditions. While the underlying etiological factors leading to impaired or complete lack of HCl secretion are not well understood, long term supplementation is safe and may be effective in certain patient populations and clinical conditions. The chemical substance hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. It is a strong acid, the major component of gastric acid and of wide industrial use. As a highly corrosive liquid, hydrochloric acid should be handled only with appropriate safety precautions.