Brain fog

What it means

Brain fog is a type of transient cognitive dysfunction that comprises a constellation of symptoms that impair intellectual functioning to a level that interferes with daily activities, commonly including forgetfulness, mental slowness, difficulty thinking or focusing, a perceived slowing of mental processing speed, inability to find the right words, a sensation that the mind went blank or is "cloudy". Brain fog tends to recur and may be triggered by factors such as physical fatigue, lack of sleep, and prolonged standing or may appear to occur spontaneously.

Brain fog has been reported in a range of diseases including myalgic encephalomyelitis/chronic fatigue syndrome, non-celiac gluten disease, postural tachycardia syndrome, lupus, and COVID-19.

Rare diseases that can present with this3

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Mental clouding · Mental fatigue · Mental fog