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Why Does COVID Cause "Brain Fog"?

New research helps explain why COVID can lead to cognitive impairments.

Wikimedia Commons, Edelmauswaldgeist, public domain.
Fog over Rattendorf.
Source: Wikimedia Commons, Edelmauswaldgeist, public domain.

My mind is in a fog, but why? And what should I do about it?

Newly announced research into the "brain fog" some experience after a mild bout of COVID-19 ties those cognitive impairments to cerebrospinal fluid abnormalities resembling those seen in sufferers of other infectious illnesses, according to researchers from UC San Francisco and Weill Cornell Medicine, New York (Leigh, 2022). Overactive immune responses may inflame brain tissue as antibodies attack the body like an autoimmune disease (Anderer, 2022). These researchers also suggest that these effects should be reversible (Hamzelou, 2022).

Though the condition lacks a clear and consistent definition, it has been researched enough to establish that it is real. Symptoms include reduced attention span, short-term memory impairment, poor executive function, and mental fatigue; it impacts perhaps 20 percent of COVID-19 patients in varying degrees long after they have overcome the physical symptoms such as fever, drainage, cough, or shortness of breath.

Deficits may begin during the physical illness, “but plenty of patients get COVID-19, recover well, and then a month or two later develop cognitive symptoms,” says Dr. Sarah A. Kremen, director of the Neurobehavior Program at the Jona Goldrich Center for Alzheimer's and Memory Disorders (Cedars-Sinai, 2021). The difficulties can last more than seven or eight months even in people without prior history of cognitive problems (Frellick, 2021). Psychotic symptoms such as hallucinations and paranoid ideation, though rare, can develop in some severe cases.

As I write this, I'm recovering from mild physical symptoms after a positive COVID-19 test. Getting the full vaccination with a booster probably helped. I had no fever, anosmia, or change in blood oxygen. Neither the congestion nor the sore throat were any worse than what my allergies sometimes put me through.

Cognitive symptoms persist, though. My range of cue utilization is restricted at the moment. I'm losing my train of thought more easily than usual, sustained attention is not easy (Zhou et al., 2020), and I have trouble processing multiple-step logic or following complicated reading material. The logic puzzles I enjoyed last month take more work now—and not in a fun way. The cognitive load tops the scale.

I find myself watching single-episode stories, specifically procedural mysteries where one step in the plot leads to the next so the viewer can follow what's happening even without solving the mystery, but trying to follow a mostly-unstructured discussion on YouTube yesterday lost me about a third of the time. From what I've read and heard, these shortcomings should all be temporary, but it's frustrating for now because I live my life immersed in thought. Thinking is living.

What Sufferers Can Do About Brain Fog

What do we do to manage this so-called "fog"? Planning ahead helps. Writing an outline, triple-checking, and getting someone else to proofread for consistency and internal logic can help me organize a blog post like this one, to make sense overall, and yet I can't write a chapter. Normally, I write chapters all the time. Today I cannot. I can edit someone else's sentences, but I have to put in extra work to see how well their overall chapter fits together. Even then, I'm still not as sure as usual.

Playing solitaire or oh-so-trendy Wordle may exercise the brain some, but probably not enough. Those games mostly rely on simple, repetitive tricks and recognition, not more complex strategy, long-term memory, or mental juggling of multiple variables. Akin to using muscles, of course, some exercise is better than none. "Use it or lose it" has proven to apply to the maintenance of a variety of skills and cognitive acuity.

“If you’re experiencing cognitive symptoms after a case of COVID-19, you should see your primary care provider,” says Kremen (Cedars-Sinai, 2021), reasonably enough. For one thing, a physician may be able to exclude other medical causes of cognitive impairment such as high blood sugar or thyroid disease. For another, the physician might help the sufferer develop a program for improvement. Still, even the medical professionals may largely be guessing about a phenomenon only recently confirmed.

One cognitive behavioral neurologist (Budson, 2021) has offered a set of tips, encouraging those with post-COVID brain fog to perform aerobic exercise, eat Mediterranean-style meals (fruits, vegetables, nuts, beans, whole grains, olive oil), avoid drugs and alcohol, sleep well, stay social, and engage in mentally stimulating activities. Without citations to back them up, it would be unclear whether all of these suggestions are empirically based, merely intuitive, or somewhat anecdotal based on one neurologist's off-the-cuff reflections. Fortunately, Budson links each recommendation to other sources. Nevertheless, should those recommendations be revised based on the past year of additional research?

Hopefully, with time, the fog will clear completely. In the meantime, take care of that brain. Continue to wear masks and follow other precautions because people can catch COVID more than once. Even a mild case can be annoying to one person yet prove fatal to someone else who catches it from them. Be careful out there.


Anderer, J. (2022, January 20). Post-COVID 'brain fog' could be result of virus changing patients' spinal fluid. CBS42.…

Budson, A. E. (2021, March 8). What is COVID-19 brain fog - and how can you clear it? Harvard Health Publishing, Harvard Medical School.…

Cedars-Sinai Staff. (2021, April 26). How COVID-19 compromises brain function. Cedars-Sinair.

Frellick, M. (2021, October 25). Brain fog can persist 8 months after COVID: Study. WebMD.

Hamzelou, J. (2022, January 20). Covid-19 brain fog: What we know about lingering neurological effects. New Scientist.…

Leigh, S. (2022, January 18). Cerebrospinal fluid offers clues to post-COVID 'brain fog.' University of California San Francisco.…

Zhou, H., Lu, S., Chen, J., Wei, N., Wang, D., Lyu, H., Shi, C., & Hu, S. (2020). The landscape of cognitive function in recovered COVID-19 patients. Journal of Psychiatric Research, 129, 98-102.