Antioxidant

An antioxidant is a molecule that neutralises free radicals and other reactive oxygen species, interrupting the chain reactions that damage skin cells, lipids and proteins. In skincare it is used mainly to defend against oxidative stress caused by ultraviolet light, pollution and normal metabolism.

Free radicals are unstable molecules that seek to grab electrons from nearby structures, degrading collagen, oxidising sebum and disrupting cell membranes. Antioxidants work by donating an electron of their own or otherwise quenching the reactive species before it spreads, which is why they are often described as sacrificial. The skin has its own antioxidant network, and topical ingredients aim to supplement it, especially in areas where its natural reserves are depleted.

Common cosmetic antioxidants include vitamin C (ascorbic acid and its derivatives), vitamin E (tocopherol), ferulic acid, niacinamide, green tea polyphenols, resveratrol and coenzyme Q10. Several of these are known to work better in combination than alone; the pairing of vitamin C, vitamin E and ferulic acid is a well-studied example of mutual stabilisation.

• Used in serums, moisturisers and, increasingly, alongside sunscreen for daytime environmental protection.
• Generally suited to most skin types, though pure high-strength forms can irritate sensitive skin.

Antioxidants complement rather than replace sun protection, and their real-world benefit depends heavily on formulation stability, since many oxidise on exposure to light and air. Products that have turned brown or changed odour have often lost potency.