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

Drinking aloe vera juice supplies your body with antioxidants that can offset harmful free radicals. —Lindsey Desoto, Health, 15 Jan. 2026

Antioxidants help fight harmful molecules called free radicals in the body. —Julie Marks, Verywell Health, 14 Jan. 2026

In addition to softening skin, tocopherol fends off free radicals found in the environment, the likes of which contribute to sunspots, sagging, and other signs of aging. —Sophie Wirt, InStyle, 5 Jan. 2026

That stress, which arises from an excess of free radicals and a dearth of anti-oxidants, causes cells to stop working and thus eventually die. —New Atlas, 4 Jan. 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