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 neutralize destructive compounds in cells called free radicals, which can cause cell damage and promote inflammation, which can lead to cardiovascular disease. —Kathi Valeii Published, Verywell Health, 8 Oct. 2025

These help prevent oxidation, chemical reactions that produce free radicals (substances that damage cells and contribute to chronic disease). —Mark Gurarie, Health, 30 Sep. 2025

And with a boost of antioxidants from La Roche-Posay’s signature thermal spring water, the face serum makes skin more resilient, protecting it from free radicals and environmental aggressors alike. —Danielle Cohen, Glamour, 18 Sep. 2025

This lightweight, silky formula pairs broad-spectrum sun protection with antioxidant-rich white tea to help fend off free radicals and environmental stressors that can accelerate visible aging. —Christa Joanna Lee, Allure, 12 Sep. 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