Antioxidants are an important class of ingredients that can both help stabilize formulations and can act as skin care actives. They inhibit the reaction of oxygen with other molecules. This reaction, called oxidation, transfers electrons from an ingredient to an oxidizing agent, producing free radicals, which in turn can start chain reactions.
Most free radicals created from oxygen atoms are called reactive oxygen species (ROS). Examples include superoxide, hydroxyl ion, singlet oxygen, and hydrogen peroxide. Hydroxyl radicals are the most destructive. Reactive nitrogen species (RNS) also cause free radical damage. Peroxynitrite is nearly as destructive as the hydroxyl radical.
Antioxidants function by slowing or preventing the oxidation of the molecules by donating hydrogen to prevent free radical formation or by neutralizing existing ones.
How Antioxidants Work
When a free radical steals an electron, a second radical is formed. This molecule in turn produces a third molecule, which generates more free radicals. This process continues until either the free radical is stabilized by a chain-breaking antioxidant such as beta-carotene, vitamins C and E, or it simply breaks down into a harmless product.
Antioxidants can prevent oxidation by reducing the rate of the chain initiation. By neutralizing the initiating radicals, antioxidants can prevent an oxidation chain from beginning. Antioxidants break the autoxidation chain reaction by donating a hydrogen atom to the lipid radical to form a stable complex. The antioxidant-free radical complex is normally adequately stable so the autoxidation chain reaction is stopped.
Autoxidation is a process of lipid peroxidation in which lipids, primarily unsaturated fatty acids, undergo a three-stage chain reaction. The three stages are:
An oxygen free radical reacts with a lipid to form a radical. Metal ions, enzymes, heat, UV light, pigments, and highly unsaturation ingredients accelerate the formation of radicals.
Lipid radicals react with Oxygen to form peroxides, which react with other fatty acids to form hydroperoxides and new fatty acid radicals.
Peroxides combine to form stable products. Hydroperoxides then decompose into aldehydes, ketones, alcohols, and acids that can produce off odors and discoloration.
Oxidative stress and skin aging
Commonly known as the free radical theory of aging, normal metabolism and environmental exposure creates free radicals. Over a lifetime, damage accumulates, leading to a decline in skin structure and function.
Chronic exposure to excessive free radicals can lead to inflammation/irritation, skin wrinkling/sagging (cross linking of proteins due to glycation) and DNA damage/reduced skin repair. Many potent anti-inflammatory agents also have good antioxidant activity. Numerous clinical studies have documented the benefits of antioxidants.
Recommended skin antioxidants based on published clinical studies include:
- FloraGLO™ (carthamus tinctorus seed oil, tagetes erecta flower extract) by Kemin – Lutein 20% topical liquid in corn oil.
- ALL-Q® Plus (ubiquinone, tocopheryl acetate, C12-15 alkyl benzoate) by DSM Nutritional Products
- Alpha Lipoic Acid (thioctic acid) by Sabinsa Cosmetics
- Stable Ascorbic Acid Derivatives – Ethyl ascorbic acid (3-0 ethyl ascorbic acid, water soluble) by Vantage Chemical and BVOSC (tetrahexyldecyl ascorbate, oil soluble) by Barnet Products.
Product stabilization (typically level .05-.1%)
Typically, the most common ingredients that require stabilization in formulations and on skin are fragrances and lipids that have a high degree of unsaturation or double bonds. This would include most natural oils, carotenoids, and retinoids. The most effective antioxidants are typically blends with chelators.
Recommended product-stabilizing antioxidants include;
- Sodium Phytate by Ankang Shi Mao Biotech/Deckner Consulting Services – A natural chelant with activity similar to disodium EDTA.
- Dissolvine® GL-47-S (glutamic acid, N.N-diacetic acid, tetra sodium salt) by AkzoNobel
- Rosamox™ Z (propanediol, rosmarinus officinalis (rosemary) leaf extract) by Kemin
- Eastman Tenox TBHQ by Eastman Chemical
- Mixed Tocopherols 95 (tocopherol) by DSM Nutritional Products
- RonaCare® AP (bis-ethylhexyl hydroxydimethoxy benzylmalonate) by EMD
- Eastman TENOX antioxidants for personal care brochure (Eastman Chemical).
- Palombo P., Fabrizi G., Ruocco V., Ruocco E., Flühr J., Roberts R., and Morganti P., Beneficial long-term effects of combined oral/topical antioxidant treatment with carotenoids lutein and zeaxanthin on human skin: A double-blinded, placebo-controlled study in humans. J Skin Pharmacol. and Physiol. 20: 199-210. 2007.
- Hoppe U.et al., Coenzyme Q, a cutaneous antioxidant and energizer, BioFactors 9 (1999) 371-378.
Beitner H., Randomized, placebo-controlled, double blind study on the clinical efficacy of a cream containing 5% alpha-lipoic acid related to photoageing of facial skin, Br. J. Dermatol. 2003 Oct;
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