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

Other examples include iron oxides — which add color to makeup and are sun- and blue light-protective — and tocopheryl acetate, a synthetic form of vitamin E that protects skin from free radicals. —Sandee Lamotte, CNN Money, 21 Oct. 2025

Chemically, roses hold powerful antioxidants that neutralize free radicals that damage collagen and speed the aging process. —Essence, 21 Oct. 2025

Antioxidants eliminate free radicals in the body and may protect against cancer and heart disease. —Danielle Zickl, Health, 20 Oct. 2025

Therefore, the researchers suggest that in pure ice, radiation byproducts such as free radicals become trapped and immobilized, slowing the chemical breakdown of biological molecules. —Samantha Mathewson, Space.com, 17 Oct. 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