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

Alongside these minerals, dark chocolate is rich in antioxidants, which help counteract free radicals—harmful molecules linked to chronic diseases. —Lana Barhum, Verywell Health, 5 Dec. 2025

The vitamin also acts as an antioxidant, helping to keep immune cells healthy by neutralizing free radicals, which are molecules found in harmful substances like pollution, cigarette smoke, and radiation that can damage cells and DNA. —Danielle Zickl, Health, 5 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

Antioxidants neutralize unstable free radicals, which can damage the body's cells. —Bryant Stamford, Louisville Courier Journal, 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