Brain fog is real. Here are the top causes

By Naveed Saleh, MD, MS
Published October 1, 2021

Key Takeaways

Although not a medical term per se, brain fog is certainly part of the public consciousness, thanks to COVID-19—which appears to affect people’s gray matter, along with the other havoc it wreaks. But other medical conditions can cause this cognitive problem, too.

Colloquially speaking, brain fog refers to thinking that is sluggish or fuzzy. In essence, it puts a damper on executive functioning, the actions of the brain that control higher-level cognition and coordinate mental abilities and behaviors.

“The term is a business metaphor, suggesting that your executive functions are akin to the chief executive that monitors all of the different departments so that the company can move forward as efficiently and effectively as possible," according to the UCSF Weill Institute for Neurosciences. “How we organize our lives, how we plan and how we then execute those plans is largely guided by our executive system.”

We all may experience a bit of brain fog from time to time, such as when we are sick with the flu, or when taking certain medications. But a number of serious conditions can cause this phenomenon and warrant further consideration. Here's a look at four causes of brain fog/cognitive impairment.  

Chemo brain

Although chemo brain goes by many names—cancer treatment-related cognitive impairment, cancer-related cognitive change, or post-chemotherapy cognitive impairment—people with the condition know exactly what others are referring to when the topic is bridged.

According to the American Cancer Society, “Most define it as a decrease in mental ‘sharpness’ and describe it as being unable to remember certain things and having trouble finishing tasks, concentrating on something, or learning new skills. Even though its exact cause isn’t known, it can happen at any time when you have cancer.”

The Society added, “These mental changes can make people unable to perform usual activities like school, work, or social activities. Or it can seem like it takes a lot of mental effort to do them. Many people don’t tell their cancer care team about their problems until it affects their everyday life. It’s important to get help and support, so be sure to let your cancer care team know if you notice any mental changes, no matter how small,”

The length of chemo brain is variable, and can be short or long-term. For most people, it doesn’t last that long, but if it does extend, quality of life is further impaired, including work, school, and social activities. As its name implies, chemo brain is usually due to chemotherapy, but other causes include hormone therapy, radiation, and surgery.

Treatments for chemo brain include cognitive rehabilitation, exercise, and meditation. Of note, cognitive rehabilitation includes activities to enhance brain function such as appreciating how the brain functions and developing strategies to absorb new information and performing new tasks, as well as continually repeating activities that become more challenging with time or employing tools to assist with organization such as planners/diaries.


A year-and-a-half into the pandemic, and it seems like there is little health damage that COVID-19 is incapable of. Add to this list brain fog.

Recent studies have demonstrated that the SARS-CoV-2 virus can lead to loss of grey matter in the brains of those before and after infection, according to a recent article published in Nature.

At the beginning of the pandemic, experts thought that the virus somehow infiltrated the brain and infected the neurons. Studies have shown, however, that the virus has trouble evading the blood-brain barrier and probably doesn’t attack the neurons. 

Instead, the virus may infect astrocytes, which support brain function, including the provision of nutrients for neurons as a means of support. The infection of astrocytes could help explain cognitive repercussions such as brain fog, fatigue, and depression.

Psychiatric conditions

In an article published in Basic and Clinical Neuroscience, Iranian researchers helped elucidate how depression, anxiety, and stress impaired executive functioning. The investigators included 448 university students—30 with depression, 27 with anxiety, and 35 with stress—and compared executive functioning in those with psychiatric symptoms vs healthy controls. 

“The results of this study substantiated that no significant differences exist among the four groups with regard to selective attention and shifting attention. After studying cognitive abilities, it became clear that the memory, inhibition control, planning and flexibility of the healthy group were better than all other groups," the authors wrote. "Also, the decision making of the healthy group was better than individuals who suffered from stress and anxiety. The decision-making of the depressed and anxiety groups was better than the stress group as well. In addition, the sustained attention of healthy people was only better than that of anxiety individuals."

The authors recommended that the students with psychiatric conditions receive appropriate treatment.

Autism-spectrum disorder

In addition to closing many schools and workplaces for extended periods of time, COVID-19 warped many social norms. These changes were rough for many, but especially for those with autism, who depend on structure and routine, according to the author of an article published in Autism Spectrum News. Of note, about 40% of people with autism-spectrum disorder (ASD) have anxiety. 

Stress related to anxiety and ASD can interfere with executive functions, such as short-term memory, planning and self-regulation. To minimize these effects, it’s best to maintain routines as much as possible, as well as scheduling time for self-care and coping throughout the day.

Share with emailShare to FacebookShare to LinkedInShare to Twitter