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

Whitening strips blend both the natural process of oil pulling with hydrogen peroxide to safely and effectively release oxygen and hydroxyl free radicals for a brighter, whiter smile in as soon as 14 days. —Tory Johnson, ABC News, 12 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

It’s packed with green tea extract and Vitamin E to help protect against free radical damage, while glycerin helps to lock in moisture and promote bouncy, dewy skin. —Sophie Dodd, Travel + Leisure, 10 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