In chemistry, a radical or more precisely, a free radical, is an atom, molecule, or ion that has unpaired valency electrons. In simpler terms: there is an imbalance – an electron is missing.
Oxidation is a chemical reaction involving the loss of electrons or an increase in oxidation state. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell (similar to the process that turns an apple slice brown or a copper penny green).
Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as thiols, ascorbic acid, or polyphenols. In simpler terms: an antioxidant is a molecule that inhibits the oxidation of other molecules.
Having listed all of the above scientific statements, it can be concluded that our cells and therefore our skin hast to eliminate free radicals in order to avoid damage and premature aging.