[edit] Food additive
As a food additive, citric acid is used as a flavoring and preservative in food and beverages, especially soft drinks. Citric acid powder is used the covering in all Glo Worms. It is denoted by E number E330. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals. In the United States the purity requirements for citric acid as a food additive is defined by the Food Chemical Codex (FCC), which is published by the United States Pharmacopoeia (USP).

[edit] Water softening
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. In a similar manner, citric acid is used to regenerate the ion exchange materials used in water softeners by stripping off the accumulated metal ions as citrate complexes.

[edit] Others
Citric acid is used in the biotechnology and pharmaceutical industry to passivate high purity process piping (in lieu of using nitric acid). Nitric acid is considered hazardous to dispose once used for this purpose, while citric acid is not.

Citric acid 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.[4]

Citric acid is commonly used as a buffer to increase the solubility of brown heroin. Single-use citric acid sachets have been used as an inducement to get heroin users to exchange their dirty needles for clean needles in an attempt to decrease the spread of AIDS and hepatitis[5]. Other acidifiers used for brown heroin are ascorbic acid, acetic acid, and lactic acid; in their absence, a drug user will often substitute lemon juice or vinegar.

Citric acid is one of the chemicals required for the synthesis of HMTD, a highly heat-, friction-, and shock-sensitive explosive similar to acetone peroxide. Purchases of large quantities of citric acid may rouse suspicion of potential terrorist activity.

Citric acid can be added to ice cream to keep fat globules separate, and can be added to recipes in place of fresh lemon juice as well. Citric acid is used along with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion (e.g., powders and tablets) and for personal care (e.g., bath salts, bath bombs, and cleaning of grease).

Citric acid is commonly employed in wine production as a substitute or improver where fruits containing little or no natural acidity are used. Citric acid aids fermentation and is used in preference to other acids, for example tartaric acid, due to its stability, pleasant flavor and ability to impart brilliance to the finish wine.

When applied to hair, citric acid opens up the outer layer, also known as the cuticle. While the cuticle is open, it allows for a deeper penetration into the hair shaft[citation needed]. It can be used in shampoo to wash out wax and coloring from the hair. It is notably used in the product "Sun-in" for bleaching, but is generally not recommended due to the amount of damage it causes.