brain fog

noun

: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly

Examples of brain fog in a Sentence

Recent Examples on the Web

Kennedy sought the advice of doctors after dealing with severe memory loss and brain fog, reportedly leading to a scan of his brain that showed a dark spot in the imagery. —Angel Saunders, PEOPLE, 15 Oct. 2025

During perimenopause, the decline in estrogen —which Noble explains as not just a hormone, but a neuroendocrine transmitter that helps the brain stay alert and energized—triggers the brain fog and can affect a variety of cognitive functions depending on the individual. —Alexa Mikhail, Flow Space, 14 Oct. 2025

There’s brain fog in there too. —Nick Caruso, TVLine, 2 Oct. 2025

The one who fights brain fog and exhaustion all day? —Alyce Collins, MSNBC Newsweek, 19 Sep. 2025

Word History

First Known Use

1853, in the meaning defined above

Rhymes for brain fog

• agog
• backlog
• bulldog
• bullfrog
• eclogue
• eggnog
• groundhog
• hedgehog
• leapfrog
• prolog
• sheepdog
• watchdog

Medical Definition

brain fog

noun

: a usually temporary state of diminished mental capacity marked by inability to concentrate or to think or reason clearly

This brain fog can be a result of being overly stressed, tired, carrying extra weight, consuming too many calories or consistently consuming a diet poor in nutrients.

—Kylie Helgens, The Gazette (Cedar Rapids, Iowa)