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
The second infection left her with brain fog and fatigue.
—
Stephanie Armour, Miami Herald, 28 Jan. 2026
The second infection left her with brain fog and fatigue.
—Stephanie Armour, CBS News, 27 Jan. 2026
Elevated resting heart rate, persistent fatigue, mood changes, brain fog, declining performance, more frequent illness, loss of appetite, recurring injuries, severe soreness, and sleep disturbances can all signal that your body needs a break.
—Danielle Zickl, Health, 20 Dec. 2025
Although hypothalamic dysfunction can trigger dozens of other symptoms, the hallmark signs are insomnia (despite exhaustion), brain fog and widespread pain, the doctor said.
—Shiv Sudhakar, FOXNews.com, 20 Dec. 2025
See All Example Sentences for brain fog
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Stephanie Armour, Miami Herald, 28 Jan. 2026
The second infection left her with brain fog and fatigue.
—Stephanie Armour, CBS News, 27 Jan. 2026
Elevated resting heart rate, persistent fatigue, mood changes, brain fog, declining performance, more frequent illness, loss of appetite, recurring injuries, severe soreness, and sleep disturbances can all signal that your body needs a break.
—Danielle Zickl, Health, 20 Dec. 2025
Although hypothalamic dysfunction can trigger dozens of other symptoms, the hallmark signs are insomnia (despite exhaustion), brain fog and widespread pain, the doctor said.
—Shiv Sudhakar, FOXNews.com, 20 Dec. 2025
See All Example Sentences for brain fog
Cite this Entry
“Brain fog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain%20fog. Accessed 30 Jan. 2026.
Copy CitationMedical 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)
Kylie Helgens, The Gazette (Cedar Rapids, Iowa)Love words? Need even more definitions?
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