Citric acid is a weak organic acid that is used in personal care products to adjust the acidity or promote skin peeling and re-growth in the case of anti-aging products.
Citric acid is widely found in both plants and animals, particularly in citrus fruits, which is what gives these fruits their characteristic acidic taste. One example is lemon juice, which contains about 5 to 8 percent citric acid. Citric acid was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice.
Interestingly, more than a million tons of citric acid are manufactured each year. There are many uses of this ingredient, including as an acidifer, as a flavoring, and chelating agent. Because it is one of the stronger edible acids, the dominant use of citric acid is as a flavoring and preservative in food and beverages, especially soft drinks and candies.
Citric acid is also well known for its use in cosmetics and personal care products. According to the 2016 U.S. Food and Drug Administration’s (FDA) Voluntary Cosmetic Registration Program (VCRP), citric acid was used in almost every category of cosmetic product with over 10,000 reported uses.
Citric acid functions as an alpha-hydroxy acid (AHA) in skin care products. AHAs are a class of chemical compounds that consist of a carboxylic acid (-COOH) substituted with a hydroxyl group (-OH) on the adjacent carbon (the alpha position). AHAs can be naturally derived from fruit and milk sugars (like citric acid from citrus fruits) or they can be synthetically produced.
AHAs are well known for their use in the skin care industry as they have been proven to reduce signs of aging, such as wrinkles, lines, and dark spots. AHAs have also been found to stimulate collagen production. A study published in the journal Dermatologic Surgery determined that AHA treatments increase the production of collagen and fibroblast proliferation both in vivo and in vitro. Collagen is found within the dermal layer of skin and it is responsible for keeping the skin smooth and firm. When the skin is stimulated to produce more collagen, fine lines and wrinkles are filled in.
According to skin care expert Paula Begoun, citric acid is also used to adjust the pH of formulations in order to prevent them from being too alkaline. The pH of cosmetics and skin care products is important because the skin’s normal pH is slightly acidic (between 4 and 6). On one hand, if a product is too acidic it may irritate the skin or cause a stinging sensation. On the other hand, a product that is too alkaline is detrimental because it depletes your skin of vital, natural fats (or “lipids”).
Despite these benefits, there are some side effects to using AHAs. A 2018 article published in the scholarly journal Molecules states that as a class, AHAs can cause swelling, burning, and itching after topical applications. Another common side effect of AHAs is photosensitivity. Since AHAs remove dead skin and some of the upper layers of skin, you may sunburn easily from very little sun exposure or from using a tanning bed.
How citric acid benefits the skin
Citric acid treatments can brighten skin, shrink pores, treat mild acne, and correct dark spots and fine lines. When applied to skin, citric acid exfoliates the top layers of skin and sloughs off dead skin cells. Additionally, the speed of new cell turnover increases, which promotes new skin growth that can help alleviate the appearance of age spots, acne scars, small wrinkles and areas of uneven tone and texture. Of note, research on the ability of citric acid to exfoliate the skin examined much higher concentrations (20% for example) than are used in skin care products.
The Cosmetic Ingredient Review (CIR) Expert Panel reviewed scientific literature and data on the safety of citric acid and its salts and ester in 2014. This data revealed that at concentrations used in cosmetics and personal care products, citric acid and its salts and esters were not eye irritants, nor did they cause skin irritation or allergic skin reactions. Thus, CIR concluded that the available scientific data showed that citric acid, its salts, and esters were safe under current conditions of use in cosmetics and personal care products.
References: Cosmetics Info, “Citric Acid”, Wikipedia, “Citric Acid”, Verywellhealth.com, “Alpha Hydroxy Acids for Wrinkles and Aging Skin”, 2017, Dermatol Surg. 1998 Oct;24(10):1054-8, Paula’s Choice, “Citric Acid”, SebaMed, “Too Acidic, Too Alkaline: The Different Dangers”, 2016, Molecules. 2018 Apr 10;23(4).