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

Flavonoids help calm chronic inflammation by lowering pro-inflammatory chemicals, neutralizing free radicals, and boosting the body’s antioxidant defenses. — Lana Barhum, Verywell Health, 4 Nov. 2026

These molecules are a kind of free radical, a broad term for a class of unstable, high-energy molecules. — Susanne Rust follow, Los Angeles Times, 29 Oct. 2026

The formula also features hyaluronic acid to boost hydration, vitamin E to defend against free radicals, and lactic acid for gentle skin-smoothing benefits. — Christa Joanna Lee, Allure, 28 Oct. 2026

Its star ingredient is a 12% concentration of L-ascorbic acid—a pure, potent form of vitamin C that brightens the complexion and neutralizes free radicals. — Jenny Berg, Vogue, 27 Oct. 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