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

Saffron is rich in antioxidants, which are believed to play a vital role in reducing inflammation and protecting the cells from damage from free radicals. — Bestreviews, Chicago Tribune, 7 Aug. 2026

Early tests suggest that the gadusol has antioxidant properties as well, kind of like vitamin C, so this could help neutralize some of those damaging free radicals that are, um, caused by sun exposure. — Popular Science Team, Popular Science, 6 Aug. 2026

Proanthocyanidins are a kind of polyphenol found in several fruit, vegetable, and seed varieties that help protect the body from oxidative stress and neutralize free radicals. — Randi Gollin, Martha Stewart, 6 Aug. 2026

Reduces Inflammation Vitamin C, lycopene, lutein, and zeaxanthin are powerful antioxidants that help fight free radicals. — Jamie Johnson, Verywell Health, 5 Aug. 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