Ascorbic acid is another name for vitamin C, an antioxidant that is popular in skin care products due to its ability to brighten skin, reduce the appearance of fine lines and wrinkles, and fade dark spots.
Ascorbic acid is a vitamin that is synthesized by most plants and animals from glucose. It is considered to be an essential nutrient because it is required for normal body functioning but cannot be synthesized by the body. Therefore, ascorbic acid must be acquired from natural sources such as citrus fruits and green leafy vegetables.
After oral intake of ascorbic acid, the absorption in the gut is limited by an active transport mechanism, which means that no matter how much ascorbic acid you ingest only a finite amount can be absorbed. Furthermore, bioavailability of ascorbic acid in the skin is inadequate when it is administered orally. Therefore, the use of topical products that contain ascorbic acid is important to reap all of the skin benefits this ingredient has to offer.
Ascorbic acid exerts potent antioxidant activity. Specifically, ascorbic acid donates electrons to neutralize reactive oxygen species (ROS) such as the superoxide ion and peroxide that are generated when the skin is exposed to UV light. This is important because the harmful effects of ROS occur as direct chemical alterations of the cellular DNA, the cell membrane, and cellular proteins, including collagen. Damaged collagen manifests as signs of premature skin aging, including wrinkles, lines, and sagging skin. Ascorbic acid’s protective effect on collagen makes this ingredient an excellent addition to anti-aging skin care products.
Another way that ascorbic acid helps to reduce signs of aging is through collagen synthesis. Specifically, ascorbic acid serves as a cofactor for the enzymes prolysyl and lysyl hydroxylase, the enzymes that are responsible for stabilizing and cross-linking the collagen molecules. Clinical studies have shown that the topical use of ascorbic acid increases collagen production in both young and aged human skin. Once again, by increasing the amount of collagen in the skin, signs of aging will be diminished and the skin will appear more firm.
In addition to anti-aging products, ascorbic acid is frequently used in skin-brightening products due to its ability to reduce the appearance of dark spots and improve uneven skin tone. This is accomplished through inhibition of melanin synthesis. Melanin is a pigment that gives our skin color, but too much of this pigment can lead to undesirable dark spots called hyperpigmentation. Ascorbic acid decreases melanin formation by inhibiting tyrosinase, an enzyme that is required for melanin synthesis. The result is skin that appears brighter with less dark spots and a more even skin tone.
While ascorbic acid is very beneficial to the skin, it is notoriously difficult to stabilize in cosmetic formulations. This is because it is such an excellent antioxidant, which means that it will readily donate electrons to the oxygen content in air. After becoming oxidized, the ascorbic acid molecule is ineffective and cannot provide skin benefits. Therefore, a product that contains ascorbic acid needs to be packaged to prevent oxidation. When purchasing a product containing ascorbic acid, make sure that the packaging is opaque and is either an airless pump bottle or a tube.
The safety of ascorbic acid and its salts has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The Panel reviewed the scientific data and concluded that these ingredients were safe for use in cosmetic and personal care products. Since ascorbic acid is an acidic ingredient, some people may experience sensitivity, redness, or stinging after using products with this ingredient. These side effects typically occur when high concentrations of ascorbic acid are used, or when ascorbic acid is combined with other ingredients that exfoliate the skin (i.e. retinol, AHAs, BHAs, etc.)
References: Wikipedia “Chemistry of ascorbic acid”, Indian Dermatol Online J 2013 Apr-Jun; 4(2): 143–146, FutureDerm “Spotlight On: L-Ascorbic Acid”