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

Niacinamide and hyaluronic acid, on the other hand, work in harmony to hydrate and boost moisture retention, and the antioxidant-rich vitamin E helps neutralize free radicals caused by UV rays. — Alicia Geigel, Southern Living, 23 July 2026

Oxidative stress occurs when free radicals exceed antioxidants, leading to damage associated with chronic diseases. — Lana Barhum, Verywell Health, 22 July 2026

It’s formulated to brighten, protect the skin barrier, and provide antioxidant support, preventing free radical damage. — Shea Simmons, PEOPLE, 18 July 2026

Oxidative stress occurs when unstable molecules called free radicals damage cells and tissues, including those in your heart and blood vessels. — Alexandria Nyembwe, Health, 16 July 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