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

Promotes Heart Health The phytochemicals (offer protection from pathogens) and antioxidants (protect the body from free radicals) in kiwifruit protect the heart. —Kathi Valeii, Verywell Health, 22 May 2025

Pollutants left on the skin can also generate free radicals that contribute to premature aging. —Lauryn Higgins, Time, 30 Apr. 2025

Remember: Antioxidants can slow aging and prevent skin damage caused by unstable molecules called free radicals. —Danielle Jackson, Glamour, 28 Apr. 2025

This antioxidant trio will help brighten dark spots and protect the skin from free radicals too. —Kristin Canning, SELF, 8 May 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