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

The echinacea plant is packed with potent antioxidants, and contains a wide net of compounds that are thought to help reduce free radicals and combat inflammation in the body, says Megan Ramaika, a bariatric dietitian at Medstar Washington Hospital Center. —Caroline C. Boyle, USA Today, 21 Nov. 2025

The hand cream has a multipurpose approach to care for your hands on all fronts, from the ceramide-rich complex that strengthens your skin’s barrier to antioxidants like purslane and vitamin E that protect the hands from free radicals. —Denise Primbet, Glamour, 18 Nov. 2025

Oxidative stress occurs when there is an imbalance of free radicals (unstable molecules) and the antioxidants that help neutralize them. —Lindsey Desoto, Health, 15 Nov. 2025

Antioxidants are compounds that fight free radicals in your body. —Kathi Valeii Published, Verywell Health, 13 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