free radical

noun

: an especially reactive atom or group of atoms that has one or more unpaired electrons

especially : one that is produced in the body by natural biological processes or introduced from an outside source (such as tobacco smoke, toxins, or pollutants) and that can damage cells, proteins, and DNA by altering their chemical structure

Examples of free radical in a Sentence

Recent Examples on the Web

Antioxidants in foods like blueberries neutralize free radicals. —Amber J. Tresca, Verywell Health, 25 Feb. 2026

Plumbody, an ultra-hydrating body cream featuring a patented ingredient called Midnight Muir, which helps reduce redness, dryness and hyperpigmentation, while fighting free radicals and enhancing skin elasticity. —Tory Johnson, ABC News, 24 Feb. 2026

Propolis, what bees use to insulate the walls of their hives to protect against outside germs, is brilliant for soothing sore throats, bolstering our immune systems, and protecting against free radicals. —Brianna Peters, Vogue, 23 Feb. 2026

Lemons are an excellent source of vitamin C, which can help support your immune system and protect your cells against damage from free radicals. —Hannah Harper, Health, 21 Feb. 2026

Word History

First Known Use

1870, in the meaning defined above

Rhymes for free radical

• radicle

Medical Definition

free radical

noun

: an especially reactive atom or group of atoms that has one or more unpaired electrons

especially : one that is produced in the body by natural biological processes or introduced from outside (as in tobacco smoke, toxins, or pollutants) and that can damage cells, proteins, and DNA by altering their chemical structure