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 lightweight, silky formula pairs broad-spectrum sun protection with antioxidant-rich white tea to help fend off free radicals and environmental stressors that can accelerate visible aging. —Christa Joanna Lee, Allure, 12 Sep. 2025

The oil-free elixir blends l-ascorbic acid, silymarin, ferulic acid, and salicylic acid to protect against free radical damage, stave off excess oil production, and clarify pores. —Akili King, Vogue, 10 Sep. 2025

Antioxidants can help protect cells from oxidative stress, which is an imbalance of free radicals and antioxidants that can lead to cell damage. —Lindsay Curtis, Verywell Health, 8 Sep. 2025

The extract also cools and is an antioxidant which protects skin from free radicals. —Kristen Philipkoski, Forbes.com, 8 Sep. 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