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

These molecules neutralize free radicals, the unstable molecules that can damage cells. —Ann Pietrangelo, Verywell Health, 27 Dec. 2025

Getting enough vitamin C protects your cells from free radicals, or highly unstable atoms. —Isabel Vasquez Rd Ldn, Health, 26 Dec. 2025

This gentle glycolic serum has salicylic acid (which exfoliates), and raspberry fruit extract (which soothes skin and protects it from free radicals). —Alanna Martine Kilkeary, Glamour, 25 Dec. 2025

Formulated with skin-nourishing ingredients like vitamin C, collagen, and sodium hyaluronate (a sister to hyaluronic acid), the serum reduces signs of aging and supports collagen production, evens your skin complexion, and defends against free radicals. —Alicia Geigel, Southern Living, 27 Nov. 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