What is brain fog?

Officially, "brain fog" isn't a medical term. "It's the colloquial jargon that patients now use to try to communicate to their doctor what's going on," Amy Arnsten(opens in new tab), a neuroscientist at the Yale School of Medicine, told Live Science.
The term is typically used to describe a constellation of persistent symptoms, including difficulty focusing, mild confusion, "fuzzy" or sluggish thoughts, forgetfulness and a general sense of fatigue. Most people have some passing familiarity with these sensations, but if these feelings become chronic they can affect a person's quality of life.
Just because brain fog lacks a strict clinical definition doesn't mean it isn't real. "I see [persistent] brain fog as a sign that something is amiss," Sabina Brennan(opens in new tab), a neuroscientist and author of the book "Beating Brain Fog(opens in new tab)" (Orion Publishing Group, 2021), told Live Science in an email.