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

This composition gives the oil both restorative and antioxidant functions, supporting skin renewal, helping to neutralize free radicals, and improving the appearance of aging over time. —Beatrice Zocchi, Vogue, 19 Feb. 2026

Instead, the chemical compounds found in the root are thought to encourage cell production and reduce the presence of free radicals in the body — two functions that may give the user a boost in energy. —Pubsubhub User, Chicago Tribune, 16 Feb. 2026

Catechins are forms of flavonoids that act as powerful antioxidants in the body to protect against free radicals. —Angelica Bottaro, Verywell Health, 10 Feb. 2026

The more free radicals in your body, the higher your oxidative stress, a response that causes damage to your cells. —Sarah Bradley, Health, 6 Feb. 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