Citric Acid or tricarboxylic acid is a weak organic acid. It is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle, and therefore occurs in the metabolism of virtually all living things. It can also be used as an environmentally benign cleaning agent.

For biological uses, Citric Acid is a critical component of bone, helping to regulate the size of calcium crystals. It is an inhibitor of phosophofructokinase, which helps regulate the rate of glycolysis (and subsequently the citric acic cycle) in the cell.

For cleaning uses, Citric Acid's ability to chelate metals makes it useful in soaps and laundry detergents. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. It is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a 6% concentration of Citric Acid will remove hard water stains from glass without scrubbing. In industry, it is used to dissolve rust from steel. It can be used in shampoo to wash out wax and coloring from the hair.

For cosmetics and pharmaceuticals uses, it is used as one of the active ingredients in the production of antiviral tissues.

For dyeing uses, Citric Acid can be used in food coloring to balance the pH level of a normally basic dye. It is used as an odorless alternative to white vinegar for home dyeing with acid dyes.

For foods, beverages and persenal care, Citric Acid is used as a flavoring and preservative in food and beverages, especially soft drinks. It can be added to ice cream to keep fat cells in food separate, and can be added to recipes in place of fresh lemon juice, as well. It is commonly employed in wine production as a substitute or improver where fruits containing little or no natural acidity are used. It is mostly used for inexpensive wines due to its low cost of production. It is one of several acids used by home brewers to modify brewing water for making beer. It may be used as the main ripening agent in the first steps of making mozzarella cheese.

For industrial and construction uses, Citric Acid is used as a successful alternative to nitric acid in passivation of stainless steel. It can be used to slow setting of portland cement. It can delay setting time substantially.

For photography uses, Citric Acid is also used as a stop bath as part of the process for developing photographic film. The developer is normally alkaline, so a mild acid will neutralize it, increasing the effectiveness of the stop bath when compared to plain water.

For safety issues, contact with dry citric acid or with concentrated solutions can result in skin and eye irritation, so protective clothing should be worn when handling these materials. Excessive consumption is capable of eroding the tooth enamel. Sometimes, a high concentration of citric acid can damage hair and bleach it.