What Is Brain Fog?

Brain fog is a well-documented symptom of chronic conditions such as fibromyalgia and Lyme disease, and of cancer treatments — it often appears after chemotherapy, previously earning it the nickname “chemo brain.” Yet it has never been formally deemed a medical condition.

That may be due to how difficult it is to diagnose: There’s no official testing protocol for brain fog, and those struggling with it may appear perfectly healthy. So, healthcare practitioners have often failed to identify — or worse, have dismissed — the condition.

That all changed in the wake of COVID-19 and, more specifically, the mysterious illness known as long COVID.

Silver Lining?

Long COVID is characterized in part by cognitive impairments that linger months after the most acute viral symptoms subside. Estimates of its prevalence vary, but a recent systematic review indicated that nearly half of those who contracted the virus continued experiencing symptoms for at least four months.

One of the most common of these symptoms is brain fog. Those who’ve suffered it have likened the experience to feeling lost, hazy, or caught in the space between sleep and waking. In some severe cases, sufferers have been forced to stop driving, reduce work responsibilities, or even halt working entirely.

If there’s a silver lining to the prevalence of cases, it’s that researchers now have a more robust dataset with which to understand how brain fog works and how it can be treated.

Causes and Treatments

Inflammation — the body’s natural, protective response to infection — was ­connected to brain fog prior to the pandemic, and it appears to be a crucial link between COVID’s initial respiratory symptoms and the longer-lasting cognitive impairments. Recent studies suggest that inflammation may spread from the lungs to other parts of the body, including the brain.

The resulting dysregulation of brain cells looks a lot like so-called chemo brain, in which damage to myelin, the fatty insulation that helps neurons efficiently transmit signals, contributes to slower processing. ­Accordingly, some researchers believe that treatments currently in development for use among chemotherapy patients experiencing brain fog may also help those with long COVID.

There’s no official testing protocol for brain fog, and those struggling with it may appear perfectly healthy. So, healthcare practitioners have often failed to identify — or worse, have dismissed — the condition.

Brain fog also resembles post­concussive syndrome, common among individuals who have experienced a traumatic brain injury (TBI). A preliminary study in which long-COVID patients were administered a combination of N-acetylcysteine, an antioxidant being tested for TBI treatment, and guanfacine, known to strengthen the prefrontal cortical circuits responsible for memory and attention, showed promise.

Because the brain communicates with all our bodily systems, conditions affecting it are notoriously difficult to understand or treat. Myriad causes may contribute to brain fog, including psychological ones.

“Things like sleep and exhaustion, pain and stress and depression — all of these nonneurological issues also play a role in our cognitive functioning,” explains Renee Madathil, PhD, a rehabilitation neuropsychologist at the University of Rochester Medical Center, in a 2021 Science magazine interview.

As we learn more about brain fog and its causes, treatment may comprise a mix-and-match approach, with pharmaceuticals, cognitive rehabilitation, and even “brain-training” games all part of the clinical toolkit.

This article originally appeared as “Cutting Through Brain Fog” in the July/August 2023 issue.