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

Antioxidants are compounds that protect cells and tissues from damaging molecules (free radicals). —Amy Brownstein, Verywell Health, 15 June 2026

Staying true to its South Asian roots, key ingredients include amla fruit extract (more commonly known as Indian gooseberry oil), which is rich in vitamin C to brighten bouts of hyperpigmentation and protect skin against free radicals (which can fast-track signs of aging). —Jailynn Taylor, Allure, 13 June 2026

This matters because antioxidants can help protect healthy cells from free radicals, or harmful molecules that cause damage. —Kirsten Nunez, Martha Stewart, 13 June 2026

Better Heart Health Green tea contains antioxidants like polyphenols and catechins, which reduce harmful compounds called free radicals in the body. —Trista Chan, Health, 10 June 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