What Are Free Radicals?
Free radicals are highly reactive molecules with one or more unpaired electrons in their outer shell. This instability drives them to steal electrons from surrounding molecules — oxidising lipids, proteins, and DNA in a destructive chain reaction. In skin, the primary free radicals generated are reactive oxygen species (ROS): superoxide anion, hydroxyl radical, hydrogen peroxide, and singlet oxygen. They are the molecular mechanism linking UV exposure and pollution to accelerated skin ageing.
How Free Radicals Form in Skin
UV radiation is the primary driver: UVA photons are absorbed by chromophores in the dermis, generating singlet oxygen and initiating an ROS cascade. Air pollutants (ozone, particulate matter, nitrogen dioxide) directly generate ROS on skin contact. Metabolic processes produce ROS as a byproduct. Infrared radiation and blue light also contribute to lower levels of free radical generation.
The Damage They Cause
ROS activate matrix metalloproteinases (MMPs) — enzymes that degrade collagen and elastin fibres, causing wrinkles and sagging. They oxidise membrane lipids (lipid peroxidation), disrupting barrier function. They damage nuclear DNA and mitochondrial DNA in skin cells, accelerating photocarcinogenesis. They oxidise melanin precursors, contributing to uneven pigmentation and dark spots.
Critical stat: A single exposure to sufficient UV radiation depletes skin antioxidant reserves for approximately 24 hours — explaining why daily antioxidant application and SPF together provide more protection than either alone.
See Antioxidants and Antioxidants in Skincare.