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

Antioxidants’ job is to counteract free radicals, which are unstable molecules that build up from stress, poor diet, or a sedentary lifestyle. — Danielle Zickl, Health, 24 June 2026

An antioxidant, the ingredient also fends off free radicals to slow hyperpigmentation, among other signs of aging. — Sophie Wirt, InStyle, 24 June 2026

Formulated with skin-nourishing ingredients like vitamin C, ceramides, hyaluronic acid, and vitamin B5, the serum reduces signs of aging and supports collagen production, evens your skin complexion, and defends against free radicals. — Alicia Geigel, Southern Living, 21 June 2026

Antioxidants are compounds that protect cells and tissues from damaging molecules (free radicals). — Amy Brownstein, Verywell Health, 15 June 2026

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