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

Kash says they are packed with antioxidants such as polyphenols and flavonoids to neutralize free radicals that cause stress and inflammation and help with boosting your immune system overall. — Marie Bladt, Vogue, 11 Aug. 2026

We can be exposed to free radicals from a number of sources including cigarette smoke, air pollution, sunlight, and even exercise. — Isabel Vasquez Rd Ldn, HEALTH, 11 Aug. 2026

This oil contains vitamin C and bakuchiol to fight free radicals, restore the skin’s elasticity, and reduce signs of aging. — Reece Andavolgyi, InStyle, 10 Aug. 2026

Saffron is rich in antioxidants, which are believed to play a vital role in reducing inflammation and protecting the cells from damage from free radicals. — Bestreviews, Chicago Tribune, 7 Aug. 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