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

By correcting the imbalance between free radicals and antioxidants (referred to as oxidative stress), the polyphenols can improve arterial function and help ease blood pressure. —Md Published, Verywell Health, 12 July 2025

Formulated with skin-nourishing ingredients like vitamin C, collagen, and sodium hyaluronate (a sister to hyaluronic acid), the serum reduces signs of aging and supports collagen production, evens your skin complexion, and defends against free radicals. —Alicia Geigel, Southern Living, 7 July 2025

These nutrients work like cellular firefighters, quenching damaging free radicals and supporting the body's natural repair mechanisms. —Ximena Araya-Fischel, Forbes.com, 4 July 2025

At high levels, free radicals trigger what’s known as oxidative stress, which can damage cell DNA and increase your risk of conditions like heart disease and diabetes.78 4. —Cynthia Sass, Health, 23 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