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

This face serum brightens and evens skin tone, fights free radicals, supports collagen production, and softens the look of fine lines and wrinkles for glowing, healthy-looking skin. —Tory Johnson, ABC News, 28 Mar. 2026

These foods work to curb cellular damage caused by free radicals, or unstable molecules that, in excess, can drive inflammation. —Lauren Manaker, SELF, 26 Mar. 2026

An antioxidant, the ingredient also fends off free radicals to slow hyperpigmentation, among other signs of aging. —Sophie Wirt, InStyle, 11 Mar. 2026

The plant pigments betalains have anti-inflammatory properties that help the body destroy free radicals. —Carrie Madormo, Verywell Health, 11 Mar. 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