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

Its antioxidant properties will help shield your skin from free radicals while hydrating heroes like glycerin and hyaluronic acid will keep your complexion nice and hydrated in the process. —Denise Primbet, Glamour, 13 Aug. 2025

Thanks to their amazing ability to neutralize free radicals, antioxidants help prevent harm to our cells and DNA. Get unlimited digital access to Vogue including the September issue for $3 $1/month for one year. —Giulia Lenzi, Vogue, 12 Aug. 2025

These properties may help reduce cellular damage caused by free radicals (unstable oxygen molecules).5 5. —Heather Jones, Verywell Health, 11 Aug. 2025

More free radicals: Damaging molecules that can inflame and age tissues. —Lucy Notarantonio, MSNBC Newsweek, 15 July 2025

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