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

Lowers Chronic Disease Risk Orange juice is rich in antioxidants, compounds that help prevent cell damage from unstable molecules called free radicals, a process known as oxidative stress. —Carrie Madormo, Verywell Health, 4 Sep. 2025

That’s not the case with this gentle toner from Renee Rouleau, which calls on antioxidant elderberry to neutralize free radicals (unstable molecules that can damage cells and contribute to aging), fight hyperpigmentation, and help promote collagen production. —Esme Benjamin, PEOPLE, 4 Sep. 2025

These antioxidants help neutralize inflammation-inducing free radicals in the body. —Caroline C. Boyle, USA Today, 28 Aug. 2025

In addition to making your eye creams work more effectively, the formula includes antioxidant-rich golden root extract to defend against free radical damage, baker’s yeast to help brighten and even tone, and golden herb extract to soothe and calm delicate skin. —Jennifer Hussein, Allure, 26 Aug. 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