What Is Brain Fog? A Detailed Scientific Guide on Limited Cognitive Function

Do you ever notice that your ability to think feels sluggish or fuzzy? You might be experiencing what’s commonly known as “brain fog.” While not technically a medical or scientific term, it describes a temporary sensation of reduced mental acuity.

Brain fog is likely as old as human intelligence, but the more recent emergence of burnout culture, which created legions of overworked achievers, brought awareness to the cognitive challenges that go with it.

When the COVID-19 pandemic hit, some people started to notice a common side effect when recovering from the virus: lingering brain fog. Since then, more research has been done to better understand brain fog, a term that’s almost as vague as brain fog itself. Read on to learn more.

Definition of Brain Fog

Brain fog isn’t something doctors diagnose their patients with. “Brain fog is a broad term used to describe some common cognitive symptoms that folks face,” says Shehroo Pudumjee, PhD, a neuropsychologist at the Cleveland Clinic Lou Ruvo Center for Brain Health in Las Vegas. These can be varied but generally center around the idea that your “thinking or memory isn’t as efficient or effective as it used to be,” she says.

“Brain fog” is thought to originate from the term “brain fag,” a phrase coined in 1850 by British physician James Tunstall, according to research. Tunstall used the term to describe the mental exhaustion that “brain workers” — lawyers, writers, teachers, students — experienced as a consequence of over studying. In the 1960s, “brain fag syndrome” was added to the DSM-4 (Diagnostic and Statistical Manual of Mental Disorders) to describe “excessive academic strain,” per research.

Today, though the common term has changed, brain fog is used to describe symptoms associated with various medical conditions, as well as a consequence of burnout and overwork in modern-day society.

Dr. Pudumjee says that brain fog manifests as “cognitive inefficiencies” — meaning, you’re having a tough time calling up your cognitive resources as well as you did in the past.

Difficulties you may notice include issues with:

• Attention
• Concentration
• Learning
• Short-term memory

What that might look like can differ between people, but here are some things you may experience as a consequence of brain fog, according to Pudumjee and Danielle Wilhour, MD, an assistant professor in neurology at the University of Colorado School of Medicine in Denver:

• You struggle with multitasking.
• You have more trouble grasping concepts or learning compared with before.
• Words arrive at the tip of your tongue, but you can’t seem to find them.
• You may feel as if you’re in a dream or trancelike state.
• You walk into a room and can’t remember what task you set to accomplish.
• You forget details of conversations.
• You can’t absorb content as well as you used to.
• You’re easily pulled off task or distracted.

Pudumjee also says that patients describe a general feeling of cognitive sluggishness. In one study that examined the use of the term “brain fog” in Reddit posts, people described this experience with a range of descriptors, including “dissociation, fatigue, forgetfulness, and excessive cognitive effort.” These symptoms can all combine to give you the feeling that your thinking is cloudy.

One of the challenges with understanding brain fog is that there are so many potential causes, and having brain fog alone doesn’t tell doctors what exactly is going on. That said, here are a few common causes to consider.

Hormonal Changes

Menopause and pregnancy can both contribute to brain fog, says Dr. Wilhour. Research shows that people who are pregnant report confusion, disorientation, and fogginess, which lead to behaviors such as putting things down in odd places, misplacing belongings, and forgetting simple work tasks. (Some call this “pregnancy brain.”)

As for menopause, one study explains that difficulty with memory can begin early on in menopause and end in postmenopause, likely due to the effects that estrogen has on memory performance.

Diet Challenges

If you’re eating a restricted diet, not consuming adequate vitamins and minerals may result in experiencing some brain fog, says Pudumjee. Specifically, a deficiency in B12 or iron can cause anemia, which can decrease your energy levels and tangentially affect cognition, says Wilhour.

In addition, food allergies and sensitivities may also change your cognitive capabilities, Wilhour notes. According to Beyond Celiac, 95 percent of people in its research with nonceliac gluten sensitivity report having brain fog.

Medications

Taking medication may include side effects related to brain fog. For example, topiramate (Topamax), which is used to treat migraine, can leave you feeling mentally murky. “I warn patients that it can cause cloudy thinking, confusion, and word-finding difficulty,” Wilhour says. In addition, taking multiple medications — also called polypharmacy — can be another factor in brain fog, she says. People experience side effects in different ways, but if you’ve noticed that brain fog has occurred after starting a new drug, ask your doctor or pharmacist if cognitive issues are a possible side effect. (Don’t stop taking prescribed meditation without first consulting your physician.)

Chemotherapy

“Chemo brain” is a well-known phenomenon that describes thinking problems before, during, and after cancer treatment, according to the National Cancer Institute. This mental fog can be caused by the cancer itself, conditions caused by cancer (such as depression or sleep problems), or a variety of treatments including chemotherapy, radiation, and hormone therapy.

Certain Medical Conditions

Wilhour notes that brain fog may emerge with many medical conditions, including postural orthostatic tachycardia syndrome, anemia, diabetes, depression, anxiety, and autoimmune conditions such as multiple sclerosis, chronic fatigue syndrome, celiac disease, and lupus.

One common disease associated with cognitive troubles: hypothyroidism, or an underactive thyroid, which affects 5 percent of Americans older than 12, per the National Institute of Diabetes and Digestive and Kidney Diseases. Fatigue, depression, and difficulty with memory and executive function are often an early sign of hypothyroidism, according to research.

Separately, researchers have found that more people with mild cognitive impairment (MCI), as opposed to those without, may develop Alzheimer’s disease or dementia, according to the National Institute on Aging. Roughly 10 to 20 percent of people 65 and older with MCI develop dementia over a yearlong period, however, studies underway aim to understand why some people with MCI progress to dementia and others don’t.

COVID-19

COVID-19 is known to cause lingering problems with attention, concentration, and memory after infection, one symptom of long COVID, according to the National Institutes of Health (NIH). This may be due to inflammation in the brain that affects how brain cells behave, according to NIH-supported research.

In one study, 7.2 percent of people who reported having long COVID experienced brain fog, and this symptom was more common in women, those who had preexisting respiratory problems, and those who had a more severe case of COVID-19.

Additionally, according to several neuroscientists and behavioral experts, the trauma and isolation some people experienced during pandemic-related lockdown may also have been a contributing factor to brain fog, notes an article in The Guardian.

If brain fog persists past a couple of weeks, talk to your doctor, advises Pudumjee. Brain fog can be normal, especially if you’re stretched thin. However, if it begins to affect your quality of life, you should seek professional medical guidance, adds Wilhour.

Your doctor will take a past medical history and (possibly) do blood work, as well as ask you questions about your lifestyle to examine your habits around physical activity, diet, stress management, and sleep. To treat brain fog, it’s important to address any existing underlying medical conditions that may be impacting your cognitive function.

Beyond that, these expert-recommended lifestyle tweaks may also help you beat brain fog.

Exercise Regularly

Stay active and aim for 150 minutes of moderate-intensity physical activity per week, if you’re healthy. (Walking counts.) “Exercise activates the brain but also tires you out, helping you sleep better at night,” says Pudumjee.

Sleep Well

Aim for at least seven hours of sleep per night, says Wilhour. And maintain a consistent rest schedule. “Go to bed and wake up at the same time,” she advises. You might want to stay up late to get more done, but it will pay off to put the laptop away or turn off Netflix. “In general, you won’t be as efficient the following day,” says Wilhour. “Sleep should be a priority for everyone.”

Manage Your Stress

Pick your favorite stress-management strategy. For instance, you could take morning walks with your neighbor, hike in nature on the weekends, practice your breathing, download books to read for pleasure, pick up a new hobby, or watch reruns of your favorite sitcom. You might also consider taking longer breaks and more vacation, as research suggests that these tactics may improve focus and well-being.

“We have a primitive brain and a more advanced brain. When in a state of chronic stress, the primitive brain takes over, and we can’t use our higher thinking functions as well,” explains Wilhour. Getting a handle on stress will help you stay more in the thinking brain.

Moderate Caffeine and Alcohol

It’s up to you if you want to include caffeine or alcohol in your life. But it’s also important to pay attention to how much and when you choose to drink those beverages. Caffeinated coffee intake is associated with a reduced risk of cognitive decline and Parkinson’s disease, according to research, but caffeinating too late in the day can cut into your sleep, says Wilhour.

If you drink alcohol, stick with moderate consumption. The Centers for Disease Control and Prevention recommends that women drink no more than one drink per day and men have no more than two drinks per day. “More can be detrimental to brain health,” says Wilhour. Drinking alcohol before bed can also affect your sleep quality; research shows that those who drink alcohol get less sleep.

Stay Connected

“We’ve evolved to be social creatures. Living an isolated life is not what the brain is meant to do,” says Wilhour. Disconnection can also contribute to depression, which can lead to brain fog, she says. One study on more than 66,000 people found that those who were most mentally fit had a combination of social connection and social engagement (versus just one or the other). Make sure to focus on your friendships and spend quality time with people you love on a regular basis.

Best Organizations

National Institute on Aging

The NIH is always a good starting point to learn more about medical concerns, and this branch of the NIH is the place to start when you’re expanding your understanding of cognitive health. You’ll learn what it means physically, mentally, and socially to take care of your brain health, as well as lifestyle habits that can impair your thinking capabilities and reasons behind cognitive decline that should prompt you to seek help.

U.S. Department of Health and Human Services

Stress is a common culprit behind brain fog, and one of the aspects of life you can work to change so you can think more clearly in the future. But managing stress isn’t always simple, which is why you need a guide to get a jump-start. You’ll learn the basics about stress (and its dangers) as well as how to plan and prepare to buffer the ill effects of stress.

Best Books

The Brain Fog Fix: Reclaim Your Focus, Memory, and Joy in Just 3 Weeks

This book by Mike Dow, bestselling author and psychotherapist, focuses on how to get your brain in shape so your life shapes up, too. You’ll take a deep dive into the brain’s inner workings to better understand what’s going on in your mind, plus a three-week plan including healthy diet, exercise, and connection to others to reclaim your sharpness.

Best Apps

Wordle

Keeping your mind engaged may help fend off cognitive fatigue, and this app by The New York Times brings the ideal mix of challenge and brevity with a new puzzle publishing every day — an incentive to come back and play often.

Stand Up! The Work Break Timer

Give your brain a break with these apps that remind you to move during a sedentary day. Customize the number of times you aim to get up throughout the hour and choose the duration so it’s suitable for your schedule. Then actually stand up or take a break to briefly unplug when prompted.