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

Plus, maca root extract protects against free radical damage, while lactic acid gently exfoliates. —Conçetta Ciarlo, Vogue, 6 Mar. 2025

Nearly all plant foods contain antioxidants, which are chemical compounds that help remove harmful free radicals from our cells.4 Luteolin is one such chemical helper. —Sarah Garone, Health, 21 Feb. 2025

Proteins that were treated continued to be fluorescent, indicating that our thiol polymer neutralized the free radical and protected the protein. —Aaron Priester, The Conversation, 19 Feb. 2025

Editor’s tip: This primer’s purple tea extract is packed with powerful antioxidants that help fight off free radicals and shield your lips from environmental stressors. —Christa Joanna Lee, Allure, 2 Mar. 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