Citric acid is a weak organic acid commonly used in the food, cosmetic and pharmaceutical industry. The parent base of citric acid, citrate, is a component of the Krebs cycle, and occurs naturally during metabolism in all living organisms. It is found naturally in citrus fruit such as lemons and limes and is used as a natural preservative. Monohydrate citric acid has one water molecule as part of it’s chemical formula, and exists as a white powder.

It can exist either in an anhydrous (water-free) form or as a monohydrate. The anhydrous form crystallizes from hot water, while the monohydrate forms when citric acid is crystallized from cold water. The monohydrate can be converted to the anhydrous form at c. 78 °C.

Cosmetics and Pharmaceuticals

• Citric acid is widely used as a pH adjusting agent in creams and gels of all kinds. In this role, it is classified in most jurisdictions as a processing aid and so does not need to be listed on ingredient lists.
• Citric acid is an alpha hydroxy acid and used as an active ingredient in chemical peels.
• Citric acid is used as one of the active ingredients in the production of antiviral tissues.