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

In addition to staving off sun damage, the non-comedogenic, non-greasy fluid works to combat breakouts and redness with azelaic acid as glycerin helps hydrate and senna alata extract protects against free radical damage. —Emily Orofino, Vogue, 29 June 2025

Over time, free radicals can cause oxidative stress that may harm your skin and cause premature signs of aging. —Kristin Canning, SELF, 19 June 2025

Others are looking to control their blood sugar or fight off free radicals in the body. —Bestreviews, Chicago Tribune, 16 June 2025

Green tea, resveratrol and a proprietary turmeric extract protect against free radicals. —Bestreviews, Chicago Tribune, 16 June 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