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

Research shows that the antioxidant and nutrient content of beets can help protect against oxidative stress, which occurs when there are too many unstable molecules known as free radicals in the body. —Angelica Bottaro, Verywell Health, 29 Jan. 2026

Antioxidant pathways are upregulated, which catalyze metabolic reactions that result in the suppression of damaging free radicals. —Scott Travers, Forbes.com, 24 Jan. 2026

In addition, chia seeds are rich in antioxidants, which can help protect blood vessels from damage caused by free radicals. —Kristen Fischer, Health, 20 Jan. 2026

Besides the powerhouse ingredient, Livaura’s formula contains green tea extract, which protects the skin from free radicals and reduces the appearance of wrinkles. —Reece Andavolgyi, InStyle, 18 Jan. 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