Lifestyle & Wellness

Brain Fog: What It Is, What Causes It, and When to Take Action

An evidence-based guide to understanding brain fog—from medical conditions and hormonal changes to lifestyle factors—plus practical strategies for clearing the mental haze.

18 min readBy Brain Zone Team

That cloudiness in your head—the moment you walk into a room and forget why, or struggle to find a word you've used a thousand times—has a name: brain fog. An estimated 28% of adults experience brain fog, making it one of the most common yet misunderstood cognitive symptoms people face today. While brain fog is not a medical diagnosis itself, it serves as an important signal that something in your body or life needs attention.

This guide explains what brain fog actually is, explores the many conditions and factors that cause it, and provides evidence-based strategies for clearing the haze. The good news: for most people, brain fog improves once its underlying cause is addressed.

What Brain Fog Actually Feels Like

Brain fog describes a constellation of cognitive symptoms that affect how clearly you think, remember, and focus. The Cleveland Clinic defines it as "a range of symptoms that cause cognitive impairment, affecting your ability to think clearly, focus, concentrate, remember and pay attention." Unlike simple tiredness, which improves with rest, brain fog often persists even after a good night's sleep.

The symptoms people describe most frequently include difficulty concentrating or focusing on tasks that should feel routine, forgetfulness and memory lapses that seem worse than usual, mental exhaustion that doesn't resolve with rest, confusion about activities you normally do without thinking, struggling to find the right words during conversation, and a sense that thoughts move more slowly than usual. People often describe the experience as feeling "cloudy," "hazy," or mentally "sluggish"—as if their mind is working through thick fog.

How Brain Fog Differs From Normal Fatigue

One critical distinction separates brain fog from ordinary tiredness. Normal fatigue resolves with adequate sleep and rest, while brain fog frequently persists regardless of how much you sleep. The exhaustion associated with brain fog is specifically cognitive—your mind feels depleted rather than your body. A 2023 study examining fatigue and cognitive symptoms found they maintain measurable differences that justify distinct recognition and assessment, even though they often occur together.

It's equally important to understand what brain fog is not. It is not a standalone medical diagnosis but rather a symptom or symptom cluster. Healthcare providers typically document it as "cognitive dysfunction" or "cognitive impairment." This distinction matters because brain fog signals that something else in the body requires investigation—whether that's a medical condition, medication side effect, or lifestyle factor.

Medical Conditions That Cloud the Mind

Brain fog frequently accompanies chronic health conditions, serving as one of the most common complaints patients report to their doctors. Understanding which conditions cause cognitive symptoms helps explain why brain fog affects so many people and why treating the underlying cause is essential.

Chronic Fatigue Syndrome and Fibromyalgia

Chronic fatigue syndrome (ME/CFS) has brain fog as one of its five core diagnostic criteria. A 2024 NIH study published in Nature Communications found abnormal functioning in the brain's right temporal-parietal area—a region involved in fatigue perception and effort—in people with ME/CFS. The mechanisms appear to involve decreased cerebral blood flow and altered neurotransmitter levels. Approximately 1% of the population, or 3.3 million Americans, lives with this condition.

Fibromyalgia produces what many call "fibro fog." The cognitive symptoms affect attention, information processing, memory, and reaction time. Contributing factors include chronic pain, poor sleep, inflammation, and sometimes the very medications used to treat the pain. The majority of fibromyalgia patients experience these cognitive difficulties daily, though the severity fluctuates alongside their other symptoms.

Autoimmune Diseases Attack Cognitive Clarity

Autoimmune conditions frequently trigger brain fog through inflammation and antibodies that reach the brain. Between 70% and 80% of people with lupus experience what's called "lupus fog" at some point in their disease course, with symptoms that wax and wane alongside disease activity. Autoantibodies reaching the brain and inflammatory cytokines appear to be the primary mechanisms behind these cognitive difficulties.

Similarly, more than half of people with multiple sclerosis experience cognitive fog as the immune system attacks the protective myelin coating on nerves. The inflammation and nerve damage directly impair the brain's ability to process information efficiently, leading to the characteristic mental cloudiness.

When Thyroid Hormones Fall Out of Balance

Thyroid dysfunction, particularly hypothyroidism, commonly causes brain fog. A study in the journal Thyroid found that even among patients taking levothyroxine for hypothyroidism, 10% to 15% report persistent brain fog despite normal thyroid hormone levels on blood tests. The active thyroid hormone T3 may not adequately reach the brain even when blood levels appear normal, leaving cognitive function impaired.

The thyroid's influence on brain function is profound. These hormones regulate metabolism in brain cells, influence neurotransmitter production, and affect how efficiently neurons communicate. When thyroid levels drop too low, thinking literally slows down at the cellular level.

Menopause Reshapes Brain Chemistry

Menopause brings cognitive changes for many women that extend beyond the occasional hot flash. Up to 60% of women report cognitive difficulties during the menopausal transition, primarily affecting verbal memory and processing speed. The cause lies in estrogen's critical role in brain function—estrogen receptors are distributed throughout brain regions crucial for memory, including the hippocampus and prefrontal cortex.

A 2024 PET imaging study from Weill Cornell Medicine found that postmenopausal women's brains compensate for estrogen loss by increasing receptor density, though this compensation correlates with lower cognitive test scores. The encouraging finding from the SWAN longitudinal study: for most women, these cognitive difficulties are temporary and don't linger long-term after the transition completes.

Diabetes and Blood Sugar Swings

Both high and low blood sugar impair cognitive function through several mechanisms. High blood sugar decreases glucose transporters in the brain, paradoxically starving it of fuel despite abundant sugar in the bloodstream. Over time, diabetes damages blood vessels that supply the brain and increases oxidative stress that harms neurons. Research has even documented hippocampal shrinkage in people with pre-diabetes. The cognitive domains most affected include memory, attention, processing speed, and executive function—precisely the areas that contribute to brain fog.

Long COVID: A Modern Epidemic of Mental Cloudiness

The COVID-19 pandemic introduced millions of people to brain fog who had never experienced it before. Close to 50% of people with long COVID report brain fog, making it one of the condition's hallmark symptoms. With an estimated 400 million people affected by long COVID globally, this represents a substantial public health concern that has accelerated research into what causes cognitive symptoms after viral infections.

Blood-Brain Barrier Breakdown

Research into long COVID brain fog has advanced rapidly, revealing multiple mechanisms at work. A landmark 2024 study published in Nature Neuroscience by Greene and colleagues used advanced MRI imaging to demonstrate blood-brain barrier disruption in patients with long COVID-associated brain fog. This barrier normally protects the brain from toxins and inflammatory molecules circulating in the blood. When it becomes "leaky," substances that don't belong in the brain gain access.

The study found elevated levels of GFAP, a protein released by damaged astrocytes (brain support cells), and increased TGFβ, an inflammatory marker, specifically in patients experiencing brain fog compared to those who recovered fully. These changes were visible in temporal and frontal brain regions up to a year after initial infection, suggesting the damage persists long after the virus itself has cleared.

Neuroinflammation Lingers

Neuroinflammation plays a central role in long COVID brain fog. NIH research shows that even mild COVID-19 infection can trigger reactive microglia—the brain's immune cells—that persist for weeks after the virus clears. These activated immune cells release inflammatory cytokines including IL-6, TNF, and a molecule called CCL11 that's linked to age-related cognitive impairment.

Researchers have also identified microclots—tiny blood clots containing trapped inflammatory molecules—in long COVID patients, with one study finding a 19.7-fold increase compared to healthy controls. However, a Cochrane review notes the evidence cannot yet definitively prove these microclots cause symptoms. The picture is complex, with a 2024 Yale study finding no significant markers of neuroinflammation in the spinal fluid of some long COVID patients with brain fog, suggesting multiple pathways may lead to similar symptoms.

Recovery Takes Time But Usually Happens

The typical trajectory shows improvement over time. Most patients see brain fog resolve within 6 to 18 months, though for some symptoms persist longer. Importantly, a systematic review and meta-analysis found that vaccination significantly reduces the risk of developing long COVID with brain fog. This provides yet another reason why vaccination matters beyond preventing acute infection.

Lifestyle Factors That Cloud Clear Thinking

Beyond medical conditions, everyday habits profoundly influence cognitive clarity. These factors are particularly important because they represent modifiable risk factors—changes you can make today that directly impact how clearly you think tomorrow.

Sleep Deprivation Erodes Cognitive Function

The research on sleep and cognition is unambiguous. Sleep deprivation impairs attention networks, executive function, and memory formation in measurable ways. Studies show that 24 hours without sleep produces cognitive deficits equivalent to a blood alcohol content of 0.05% to 0.1%—legally drunk in most places. Even if you feel mentally alert, your brain is performing as if impaired.

The mechanisms are equally clear. During sleep, the brain's glymphatic system clears metabolic waste, including beta-amyloid proteins associated with Alzheimer's disease. Sleep deprivation impairs this cleaning process and reduces glucose metabolism throughout cortical and subcortical brain regions. Even moderate sleep restriction—getting 1.5 hours less than your body needs over six weeks—erases improvements in working memory and cognitive control that would otherwise occur.

Chronic Stress Physically Changes the Brain

The Framingham Heart Study, examining over 2,200 people, found that those with the highest cortisol levels—the stress hormone—had worse memory and visual perception, plus lower total brain volumes, particularly in the frontal and occipital lobes. A 20-year prospective study linked high chronic stress to hippocampal atrophy and reduced gray matter in the orbitofrontal cortex, brain regions critical for memory and decision-making.

The mechanisms involve cortisol disrupting neurotransmitter balance, triggering neuroinflammation, and directly suppressing the birth of new neurons in the hippocampus. Interestingly, the Framingham study found this effect was stronger in women than men, though the reasons for this difference remain under investigation.

Nutritional Deficiencies Starve the Brain

Vitamin B12 deficiency deserves particular attention for its cognitive effects. A study of 202 cognitively impaired patients with low B12 found that supplementation improved cognition in 84% and improved memory, language, and attention test scores in 78%. Even more concerning, a 2025 UCSF study revealed that even B12 levels considered "healthy" by standard measures may be insufficient—participants with lower (but technically normal) B12 showed significant delays in visual processing and more white matter lesions on brain scans.

Vitamin D receptors exist throughout the brain, and deficiency has been linked to impaired executive function and reduced hippocampal volume. Iron deficiency anemia commonly causes cognitive symptoms, particularly affecting memory, attention, and behavior. The brain requires these nutrients to function optimally, and even marginal deficiencies can manifest as mental fog.

Dehydration Shrinks Brain Tissue

Even mild dehydration alters brain structure and function in ways you can't feel directly but that show up on brain scans and cognitive tests. Neuroimaging studies show that dehydration causes the brain's ventricular system to expand as brain tissue shrinks. An fMRI study found that dehydrated adolescents showed stronger brain activation during cognitive tasks without actually performing better—their brains had to work harder for the same output. While some studies show no cognitive effects at mild dehydration levels, the elderly appear particularly vulnerable to even small fluid deficits.

When Depression and Anxiety Cloud Your Mind

Depression and anxiety don't just affect mood—they directly impair cognition through changes in brain chemistry and structure. Understanding this connection matters because these conditions are treatable, and cognitive symptoms often improve significantly with appropriate treatment.

Depression Can Mimic Dementia

Depression can cause what clinicians call "depressive pseudodementia"—cognitive impairment severe enough to mimic neurodegenerative dementia but that is largely reversible with treatment. Estimates suggest 2% to 32% of older adults with apparent cognitive problems actually have pseudodementia rather than true dementia. A key distinguishing feature helps doctors tell them apart: people with depressive pseudodementia typically complain about their memory problems and may even exaggerate deficits, while those with true dementia often try to hide or minimize them.

One study found 53% of patients with depressive cognitive disorder showed complete resolution of dementia symptoms with antidepressant treatment. This highlights why thorough evaluation matters—what looks like irreversible cognitive decline may actually be treatable depression.

Anxiety Competes for Mental Resources

Anxiety impairs working memory and attention through well-documented mechanisms. A meta-analysis of 177 samples found a reliable association between higher anxiety and lower working memory performance. In people with generalized anxiety disorder, difficulty concentrating is present at clinically significant levels in approximately 90% of patients. The mechanism involves threat-related information competing with cognitive tasks for limited mental resources—your brain is so busy scanning for danger that it can't fully focus on the task at hand.

Burnout Causes Measurable Deficits

A meta-analysis of 17 studies comparing burnout patients to healthy controls found moderate effect sizes for impairments in episodic memory, working memory, executive function, attention, and processing speed. The encouraging finding: unlike major depression, where cognitive deficits can persist after mood improves, executive function impairment during burnout can recover to the level of healthy controls once burnout resolves. This suggests the cognitive symptoms of burnout are more state-dependent and reversible.

Medications That Fog Your Brain

Many common medications list cognitive side effects that may not be obvious when you first start taking them. Awareness of which medications commonly cause brain fog can help you have productive conversations with your healthcare provider about alternatives when cognitive symptoms become problematic.

Anticholinergic Drugs Block Memory Chemicals

Anticholinergic medications block acetylcholine, a neurotransmitter essential for memory and learning. This large category includes first-generation antihistamines like diphenhydramine (Benadryl), overactive bladder medications like oxybutynin, tricyclic antidepressants, and some sleep aids. Second-generation antihistamines like loratadine (Claritin) and cetirizine (Zyrtec) have fewer cognitive effects because they don't cross the blood-brain barrier as readily.

Older adults taking multiple anticholinergic medications face particular risk. Research has linked chronic use to increased dementia risk, though whether the medications cause dementia or people with early cognitive decline are simply prescribed more of these medications remains debated.

Chemotherapy Creates "Chemo Brain"

Chemotherapy frequently causes "chemo brain." Up to 75% of patients experience some cognitive impairment during treatment, with 13% to 70% reporting lasting effects depending on the study and cancer type. The mechanisms include neuroinflammation, oxidative stress, and blood-brain barrier disruption. A 2022 NCI study identified a specific pathway—involving a molecule called S1P—that might eventually be targeted to prevent these effects, offering hope for future interventions.

Common Medications With Cognitive Effects

Benzodiazepines (Ativan, Xanax) used for anxiety, opioid pain medications, corticosteroids at high doses, and beta-blockers can all cause cognitive symptoms. Even proton pump inhibitors for acid reflux have been linked in some studies to increased dementia risk, though research findings are mixed and the absolute risk increase, if real, appears small.

Recognizing When Brain Fog Needs Medical Attention

Brain fog warrants a conversation with a healthcare provider when it persists beyond several weeks, interferes with work performance or daily activities, or occurs alongside other concerning symptoms. The evaluation process aims to identify treatable underlying causes that, once addressed, often resolve the cognitive difficulties.

Warning Signs Requiring Urgent Evaluation

Seek urgent medical evaluation for sudden onset of cognitive symptoms, which could indicate stroke or other acute problems. Confusion accompanied by severe headache or fever raises concern for infections like meningitis. Focal neurological deficits like weakness on one side, vision changes, or difficulty speaking require emergency assessment. Rapidly worsening symptoms over days rather than weeks also warrant same-day medical attention.

What to Expect During Evaluation

During evaluation, doctors typically take a detailed history of when symptoms started, what makes them better or worse, and what other medical conditions or medications might be contributing. A neurological examination checks for subtle signs of dysfunction. Bloodwork commonly checks thyroid function, vitamin levels (B12, D, folate), blood sugar, inflammatory markers, and organ function that might affect cognition.

Cognitive screening tools like the Montreal Cognitive Assessment (MoCA) help quantify impairment objectively, while formal neuropsychological testing provides detailed evaluation when screening suggests problems. Imaging studies like MRI are reserved for cases with concerning features like sudden onset, focal neurological findings, or cognitive decline that doesn't fit a clear pattern.

Evidence-Based Strategies for Clearing the Fog

The strongest evidence supports lifestyle interventions that address the factors we can control. These strategies benefit brain health broadly while specifically targeting common contributors to brain fog. The key is addressing multiple factors simultaneously rather than expecting a single intervention to solve the problem.

Prioritize Sleep as Foundation

Sleep remains the most fundamental cognitive health intervention. Aim for 7 to 9 hours nightly, maintain consistent sleep and wake times even on weekends, and practice good sleep hygiene: keep your bedroom dark and cool, avoid screens for at least an hour before bed, and limit caffeine after early afternoon. For persistent insomnia, cognitive behavioral therapy for insomnia (CBT-I) outperforms medication in clinical trials for producing lasting improvements.

Exercise Produces Robust Cognitive Benefits

A systematic review of 54 randomized controlled trials found that exercise improves all cognitive domains: executive function, memory, attention, and processing speed. The optimal dose appears to be 724 or more MET-minutes per week, roughly equivalent to 30 minutes of moderate activity most days. Both aerobic exercise like brisk walking or cycling and resistance training like weight lifting contribute to cognitive benefits, with combination approaches showing the strongest effects.

Eat for Brain Health

Mediterranean-style eating patterns show 11% to 30% reduced risk of cognitive impairment across meta-analyses. The key components include fruits, vegetables, fish rich in omega-3 fatty acids, olive oil, nuts, and whole grains, while limiting processed foods, refined carbohydrates, and excessive sugar. This isn't about following a strict diet but rather shifting the balance of what you eat toward whole foods and away from processed options.

Manage Stress Mindfully

A meta-analysis of 111 randomized controlled trials found that mindfulness-based interventions produce small-to-moderate improvements in executive attention, working memory accuracy, and cognitive flexibility. Practical stress management doesn't require hours of meditation—even brief daily practice helps. Box breathing for acute stress (inhale for four counts, hold for four, exhale for four, hold for four) activates the parasympathetic nervous system and reduces cortisol levels.

Use Cognitive Compensation Strategies

While addressing root causes, cognitive compensation strategies help manage symptoms day-to-day. Write things down rather than relying on memory for important tasks. Use calendars and reminders consistently rather than trying to keep everything in your head. Reduce multitasking and minimize distractions when you need to focus—turn off notifications and close unnecessary browser tabs. Take regular breaks during cognitive work, following something like the Pomodoro Technique of 25 minutes focused work followed by 5-minute breaks. Establish consistent routines for daily activities to reduce the cognitive load of constant decision-making.

Finding Clarity Again

Brain fog is a real and common experience affecting roughly one in four adults, but it is a symptom requiring investigation rather than a diagnosis to accept and live with. The causes span medical conditions including autoimmune diseases, hormonal changes, long COVID, and diabetes; lifestyle factors like sleep deprivation, chronic stress, and nutritional deficiencies; mental health conditions including depression, anxiety, and burnout; and numerous medications.

The path forward involves identifying and addressing underlying causes while implementing evidence-based lifestyle strategies. Strong research supports prioritizing 7 to 9 hours of quality sleep, regular exercise combining aerobic and resistance training, a Mediterranean-style diet, and stress management. For persistent symptoms, medical evaluation can identify treatable conditions from thyroid dysfunction to vitamin deficiencies to sleep apnea.

Perhaps most importantly, brain fog from most causes improves with appropriate intervention. The cloudiness you're experiencing now doesn't have to be permanent—understanding what's causing it is the first step toward clearing your mind and reclaiming the mental clarity you deserve.

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