Citric acid is a natural substance produced in various amounts by all types of citrus fruits. Common natural sources of the ingredient include lemons, limes, oranges and grapefruits. The bitter taste of citric acid makes it a common additive in foods and beverages, and its chemical properties are beneficial in skin care products. Its importance as an ingredient has led to the massive production of citric acid around the world; more than 1 million tons of the acid are manufactured worldwide each year.
The Persian alchemist Jābir ibn Hayyān, who lived during the 8th century, is credited with the initial discovery of citric acid. By the medieval age, scholars in Europe had also discovered the acid and wrote extensively about it early scientific texts. Although the existence of citric acid was well established, it took nearly a thousand years from the first discovery of the ingredient to the first successful isolation of the acid from fruits. It was the Swiss scientist Carl Wilhelm who finally managed to extract the acid in 1784.
Even after citric acid was isolated, obtaining enough of the acid for use on a wide scale proved difficult. It was not until 1893 that a possible solution was found when scientist C. Wehmer discovered that fermenting sugar with the mold Penicillium could produce citric acid. After World War I made it difficult to obtain the citrus fruits needed to extract citric acid, scientists began investigating Wehmer's findings, and in 1917 the scientist James Currie found that the fungus Aspergillus niger was incredibly useful as a fermenting agent in the production of citric acid. To this day, this fungus is still the chief material used in the industrial manufacturing of citric acid.
In its raw state, citric acid is often used to adjust the pH of skin care products. Adding the ingredient to a formula makes it slightly more acidic and can help other ingredients in a particular product function more optimally. Under the labeling regulations established by the U.S. Food and Drug Administration, citric acid does not need to be listed on the packaging of products that use the ingredient simply as a pH adjuster, and as a result, many people use citric acid every day in their cleansers and soaps, toners, moisturizers, hair care products and cosmetics without ever knowing it. The acid is also crucial for ensuring the desired color results from many hair dyes.
Citric acid is a member of the alpha hydroxy acid family of molecules. This class of acids is widely used in skin care products that are meant to exfoliate the complexion. When applied to the skin in a concentrated dose, citric acid breaks down the protein bonds between dead and living skin cells, causing the older, dead cells to be shed. Alpha hydroxy acids like citric acid are included in over-the-counter products and in clinical chemical peels that are used to resurface the complexion to eliminate fine lines, wrinkles, scars and areas of skin discoloration. By removing the dead cells that often clog the pores, citric acid can also be beneficial for people suffering from acne or enlarged pores.
In addition to its usefulness in its raw state, citric acid can be combined with minerals and compounds to form ingredients that offer additional benefits for the skin. Esters formed from citric acid create a thin protective coating on the skin that limits how much moisture evaporates from the tissue into the air. This makes the citric acid esters like tricaprylyl citrate effective ingredients in moisturizers. The esters of the acid also help to soften the skin, providing additional moisturizing benefits.
Aluminum mixed with citric acid forms a substance called aluminum citrate and is used as an astringent in skin care products. Products that contain aluminum citrate help to shrink the pores and are useful for combating pore enlargement as well as for treating acne and improving the look and feel of oily and combination skin. Another derivative of citric acid, ethyl citrate creates a stiff covering when sprayed onto the hair and is a common ingredient in hairsprays. A combination of zinc and citric acid, zinc citrate helps to prevent the formation of tartar on the teeth and is a common ingredient in natural toothpastes and teeth whiteners.