What Is Brain Fog

What Is Brain Fog? Understanding This Common Cognitive Symptom

Have you ever walked into a room and completely forgotten why you went there? Or struggled to find the right words during a conversation? While everyone experiences occasional mental lapses, some people deal with persistent cognitive difficulties that feel like thinking through a thick haze. This phenomenon, commonly known as “brain fog,” affects more than a quarter of adults and can significantly impact daily life, work performance, and overall wellbeing.

What Is Brain Fog?

Brain fog isn’t a medical diagnosis but rather a colloquial term describing a constellation of cognitive symptoms that make you feel mentally “cloudy” or unable to think clearly. Research characterising brain fog across nearly 26,000 participants found it’s best described as difficulty concentrating or focusing, often accompanied by problems with memory, slower processing speed, and communication challenges.

The term itself emerged from the German concept of “clouding of consciousness” and has been used in various medical contexts for over a century. Today, it has gained widespread recognition, particularly following the COVID-19 pandemic, though it’s associated with numerous other conditions as well.

The Core Symptoms of Brain Fog

According to large-scale research studies, people experiencing brain fog commonly report:

• Difficulty focusing or concentrating (the most strongly associated symptom)
• Slowed thinking and processing speed
• Memory problems, particularly with short-term recall
• Trouble finding words or following conversations
• Mental fatigue that worsens throughout the day
• Difficulty multitasking or managing multiple inputs
• Problems with decision-making and planning
• Feeling mentally “disconnected” or confused

These symptoms often fluctuate in severity, with many people experiencing “good days” and “bad days” without clear triggers.

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What Does Brain Fog Feel Like?

Understanding the subjective experience of it helps illuminate why it’s such a frustrating condition. People describe it in remarkably similar ways across different underlying causes:

First-Person Descriptions

Research exploring patient experiences reveals the varied nature of brain fog:

“I can’t cope with multiple inputs, like if I’m trying to reply to a message on my phone and one of my boys starts speaking to me or there’s something else happening as well that just really fries my brain.”

“You know what you want to say but you can’t think what that word is because it doesn’t come to the forefront of your mind.”

Many describe a sensation of mental “fuzziness” or pressure inside their head, as if looking at life through a haze or functioning with a mind full of cotton. Some report feeling their thoughts are moving too slowly, while others describe thoughts “rushing” in an uncontrolled manner.

The Variability Factor

One of the most challenging aspects of brain fog is its unpredictability. The cognitive difficulties can:

• Fluctuate throughout the day
• Worsen with physical or mental exertion
• Improve with rest (though not always)
• Last hours, days, or even persist for years
• Occur episodically, disrupting periods of normal function

This variability makes it particularly difficult to manage and can lead to frustration when trying to explain it to others.

Brain Fog vs. Normal Forgetfulness: What’s the Difference?

Everyone experiences occasional mental lapses—forgetting where you put your keys or losing your train of thought. So how do you know if what you’re experiencing is normal or brain fog?

Key Distinguishing Features

Normal forgetfulness:

• Occasional and brief
• Doesn’t significantly impact daily functioning
• Often related to specific factors (lack of sleep, stress)
• Resolves with rest or removal of the stressor

Brain fog:

• Persistent or recurring over weeks to months
• Significantly impacts work, relationships, or daily activities
• May not have an obvious trigger
• Often accompanies other symptoms like fatigue or mood changes
• Can persist despite adequate rest

Research shows that brain fog is associated with measurable cognitive changes—people with it scored 0.1 standard deviations lower on cognitive tests, with the largest deficits appearing in tasks requiring cognitive flexibility and the ability to inhibit distracting information.

What Causes Brain Fog?

It isn’t a single condition but rather a symptom associated with numerous underlying causes. Understanding what triggers brain fog is crucial for finding effective solutions.

Common Medical Conditions Associated with Brain Fog

Research has identified brain fog as a prevalent symptom across more than a dozen chronic conditions:

Post-viral conditions (28-30% prevalence):

• Long COVID-19 (one of the most common persistent symptoms)
• Post-viral fatigue syndromes
• Chronic fatigue syndrome/Myalgic encephalomyelitis (ME/CFS)

Neurological conditions:

• Concussion and traumatic brain injury (65% prevalence)
• Migraines (strongly associated via disability scores)
• Multiple sclerosis
• Post-stroke syndrome

Autoimmune and inflammatory conditions:

• Systemic lupus erythematosus (“lupus fog”)
• Fibromyalgia (“fibro-fog,” 76-83% prevalence)
• Rheumatoid arthritis

Hormonal conditions:

• Menopause and perimenopause (68% prevalence)
• Hypothyroidism
• Adrenal insufficiency

Other medical conditions:

• Cancer and chemotherapy (“chemofog,” 44% in breast cancer)
• Chronic kidney disease
• Sleep disorders (96% in central narcolepsy)
• Postural tachycardia syndrome (POTS)
• Coeliac disease

The Gut-Brain Connection

Emerging research highlights the critical role of gut health in cognitive function. The gut-brain axis—the bidirectional communication system between your digestive system and brain—plays a significant role in brain fog for several reasons:

Inflammation: Gut inflammation can trigger systemic inflammation that affects brain function. Studies show that inflammatory markers are associated with both brain fog symptoms and cognitive performance deficits.

Nutrient absorption: Poor gut health can impair absorption of essential nutrients needed for optimal brain function, including B vitamins, omega-3 fatty acids, and minerals like iron and zinc.

Microbiome imbalance: Your gut microbiome produces neurotransmitters and metabolites that directly influence brain function. Disruptions in the microbiome composition (dysbiosis) have been linked to cognitive symptoms.

Small intestinal bacterial overgrowth (SIBO): This condition, where excessive bacteria colonize the small intestine, can cause it through multiple mechanisms including nutrient malabsorption, bacterial toxin production, and increased intestinal permeability (“leaky gut”).

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Lifestyle and Environmental Factors

Beyond medical conditions, several lifestyle factors can trigger or worsen it:

• Poor sleep quality (strongly correlated with brain fog across studies)
• Chronic stress and anxiety
• Depression (one of the strongest correlates of subjective brain fog)
• Nutritional deficiencies
• Dehydration
• Alcohol consumption
• Certain medications
• Environmental toxin exposure
• Sedentary lifestyle

The Science Behind Brain Fog: What’s Happening in Your Brain?

While brain fog is subjectively experienced, research has identified several objective changes in the brain associated with these symptoms.

Cognitive Performance Changes

Studies using comprehensive cognitive testing reveal that people with brain fog show subtle but measurable deficits in:

Processing speed: Tasks take longer to complete, even when accuracy is maintained.

Attention and executive function: The most consistent finding across conditions is impaired sustained attention and difficulty inhibiting distracting information. Modified Stroop tests (which measure the ability to focus on relevant information while ignoring irrelevant cues) show the largest deficits.

Working memory: Difficulty holding and manipulating information in mind for short periods.

Episodic memory: Some studies show problems with delayed recall, though this is less consistent than attention deficits.

Importantly, these deficits are generally small—it doesn’t cause dementia-level impairment but rather subtle decrements that can still significantly impact daily functioning.

Neurobiological Mechanisms

Research has identified several potential biological mechanisms underlying brain fog, though these vary by condition:

Blood-brain barrier dysfunction: Studies in long COVID patients with brain fog found increased permeability of the blood-brain barrier, potentially allowing inflammatory molecules to affect brain function.

Neuroinflammation: Multiple conditions associated with brain fog show evidence of increased inflammatory markers, both systemically and in the brain.

Altered cerebral blood flow: Reduced blood flow to the brain has been documented in conditions like ME/CFS and POTS.

Neurotransmitter imbalances: Changes in serotonin, dopamine, and other neurotransmitter systems may contribute to symptoms.

Mitochondrial dysfunction: Some research suggests impaired cellular energy production may underlie the fatigue and cognitive symptoms.

Structural brain changes: While subtle, some studies show reduced gray matter volume or altered connectivity in brain regions involved in attention, memory, and executive function.

The Role of Non-Cognitive Factors

Interestingly, research consistently shows that it is influenced by factors beyond pure cognitive impairment:

Fatigue: One of the strongest correlates of brain fog across all conditions. The relationship is so strong that some researchers consider brain fog a cognitive manifestation of fatigue.

Mood and anxiety: Depression and anxiety symptoms are strongly associated with subjective brain fog reports, often mediating the relationship between underlying conditions and cognitive complaints.

Pain and physical symptoms: In conditions like fibromyalgia, physical symptoms and distraction by pain contribute to cognitive difficulties.

Sleep quality: Poor sleep both contributes to and exacerbates brain fog.

This multifactorial nature means that addressing brain fog often requires a comprehensive approach targeting multiple contributors simultaneously.

How Common Is Brain Fog?

It is remarkably prevalent, affecting a significant portion of the population:

• General population: 28.2% report experiencing brain fog
• Long COVID: 20-30% of people post-COVID infection
• ME/CFS: 85-89% report cognitive symptoms
• Fibromyalgia: 76-83% report cognitive difficulties
• Menopause: 68% during perimenopause
• Post-concussion: 65%
• Cancer patients: 44% during chemotherapy for breast cancer

These numbers suggest that most people will experience a condition or situation that could result in brain fog at some point in their lives.

Who Is Most Affected?

Large-scale research reveals certain demographic patterns:

Age: People with brain fog tend to be slightly older on average (mean age 35.7 years vs 32.8 years for those without), though this doesn’t suggest age-related cognitive decline. Brain fog can affect people of all ages.

Sex: Women are more likely to experience it (odds ratio 1.2), which may relate to hormonal factors, higher rates of autoimmune conditions in women, or differences in symptom reporting.

Education level: Interestingly, education level doesn’t appear to be associated with it, suggesting it’s not simply a matter of cognitive reserve.

Brain Fog and Daily Life: The Real-World Impact

The subjective nature of brain fog might lead some to dismiss it as trivial, but research clearly demonstrates significant real-world consequences:

Occupational Impact

Brain fog can severely affect work performance and career:

• Reduced productivity: Difficulty completing tasks efficiently
• Increased errors: Problems with paperwork, calculations, and detail-oriented work
• Impaired decision-making: Difficulty planning and prioritising
• Communication challenges: Trouble following conversations in meetings or expressing ideas clearly
• Extended absences: Some people cannot return to work due to cognitive difficulties
• Career changes: Forced to leave cognitively demanding roles

Studies show strong associations between it and difficulties with:

• Completing paperwork (odds ratio 1.8)
• Mental arithmetic (odds ratio 1.8)
• Planning ahead (odds ratio 1.7)
• Driving (odds ratio 1.6)

Social and Relationship Effects

It extends beyond work to personal relationships:

• Difficulty following conversations, leading to social withdrawal
• Forgetting appointments and commitments (odds ratio 1.9)
• Parenting challenges, including reduced ability to multitask with children
• Strained relationships due to perceived inattentiveness or unreliability
• Social isolation from feeling unable to keep up with social interactions

Psychological Impact

The cognitive difficulties and their consequences take a psychological toll:

• Anxiety and depression: It is strongly associated with both anxiety and depressive symptoms
• Reduced self-efficacy: Feeling incapable or unreliable
• Loss of identity: Particularly for those who prided themselves on mental sharpness
• Frustration and irritability: Difficulty managing emotions (odds ratio 1.6 for feeling irritable)
• Guilt and shame: About reduced capabilities

Research shows that changes in cognitive functioning, including brain fog, are related to the development of psychological disorders, creating a potential cycle where brain fog contributes to mood problems, which in turn worsen brain fog.

How Is Brain Fog Diagnosed?

Currently, there’s no single diagnostic test. The term itself isn’t a formal medical diagnosis but rather a descriptive symptom. However, healthcare providers can assess for it and its potential causes through several approaches:

Clinical Assessment

Symptom characterisation:

• Detailed discussion of cognitive symptoms
• Timeline and pattern of symptoms
• Impact on daily functioning
• Associated symptoms (fatigue, mood changes, physical symptoms)

Cognitive screening:

• Brief cognitive tests in the office
• Standardised questionnaires about subjective cognitive function
• More comprehensive neuropsychological testing if indicated

Identifying underlying causes:

• Medical history review
• Physical examination
• Laboratory tests (thyroid function, vitamin levels, inflammatory markers, gut function etc.)
• Imaging studies if neurological causes suspected

Self-Report Measures

Several validated questionnaires have been developed to assess brain fog, though none is universally used:

• Brain Fog Scale: Assesses cognitive symptoms, fatigue, affect, and sleep
• Mental Clutter Scale: Focuses on the subjective “fogginess” experience
• Fatigue and Altered Cognition Scale (FACs): Combines fatigue and cognitive symptoms
• Neuro-QoL Cognition Short Form: Measures cognitive quality of life

The Challenge of Measurement

One complicating factor in diagnosing brain fog is the often-weak correlation between subjective symptoms and objective cognitive test performance. Many people with significant brain fog complaints perform within normal ranges on standard neuropsychological tests, while others show measurable deficits.

This disconnect doesn’t mean brain fog “isn’t real”—rather, it suggests that:

1. Standard cognitive tests may not capture the specific impairments people experience in daily life
2. Factors like fatigue, mood, and metacognitive errors contribute to the experience
3. The fluctuating nature of brain fog may not be apparent during a single testing session

What Does Brain Fog Feel Like? Understanding Different Presentations

While brain fog shares common features, the exact experience varies based on the underlying cause and individual factors.

Brain Fog After COVID-19

Post-COVID brain fog is one of the most researched presentations due to its recent prevalence:

• Often begins during acute infection and persists for months or years
• Characterised by difficulty concentrating, memory problems, and mental fatigue
• May fluctuate with post-exertional malaise (worsening after physical or mental activity)
• Commonly accompanied by fatigue, headache, and anxiety
• Associated with measurable deficits in processing speed and attention

The mechanisms may include ongoing inflammation, blood-brain barrier dysfunction, and microvascular changes.

Brain Fog in Menopause

Perimenopausal brain fog has distinct characteristics:

• Often described as difficulty with word-finding and “tip of the tongue” experiences
• Problems with short-term memory (“Why did I come into this room?”)
• Difficulty concentrating on complex tasks
• May correlate with hot flashes and sleep disturbances
• Related to hormonal fluctuations affecting brain regions involved in memory

Research shows that while subjective complaints are common, objective deficits are more subtle and may improve post-menopause.

Brain Fog in Autoimmune Conditions

“Lupus fog” and “fibro-fog” share features:

• Chronic, persistent cognitive difficulties
• Strong association with pain, fatigue, and mood symptoms
• Difficulty with sustained attention and multitasking
• Variable day-to-day severity
• May be influenced by disease activity and inflammation

Brain Fog Related to Gut Health

When brain fog stems from gut issues like SIBO or dysbiosis, additional features may include:

• Association with digestive symptoms (bloating, pain, irregular bowel movements)
• Potential worsening after eating certain foods
• Improvement with gut-directed treatments
• Accompanying nutritional deficiencies

How to Get Rid of Brain Fog: An Overview

While we’ll cover this topic in depth in a future article, here’s a brief overview of evidence-based approaches:

Treating Underlying Conditions

The most effective strategy is identifying and treating the root cause:

• Managing autoimmune disease activity
• Hormone support/replacement for thyroid or menopausal issues
• Addressing sleep disorders
• Treating depression and anxiety
• Managing chronic pain

Lifestyle Interventions

Research supports several non-pharmacological approaches:

Physical activity: Regular exercise has shown benefits across multiple conditions associated with brain fog, potentially improving cerebral blood flow, reducing inflammation, and supporting neuroplasticity.

Sleep optimisation: Improving sleep quality through sleep hygiene, treating sleep disorders, and maintaining consistent sleep schedules.

Stress management: Mindfulness, meditation, and stress-reduction techniques may help reduce brain fog associated with anxiety and stress.

Dietary approaches: Anti-inflammatory diets, ensuring adequate hydration, and addressing nutritional deficiencies.

Cognitive rehabilitation: “Brain training” exercises and cognitive behavioural therapy show promise in some conditions.

The Gut Health Connection

For many people, addressing gut health is a crucial component of brain fog treatment:

Identifying imbalances: Testing for SIBO, dysbiosis, and intestinal permeability provides valuable information about potential gut-related contributors.

Targeted supplementation: Probiotics, prebiotics, and supplements to address specific deficiencies or support gut healing may be beneficial.

Dietary modifications: Eliminating trigger foods, following specific therapeutic diets (low-FODMAP, Mediterranean, anti-inflammatory), and supporting gut barrier function.

Treating gut conditions: Addressing SIBO, candida overgrowth, parasites, or other identified gut issues.

Pharmacological Options

In some cases, medications may be helpful:

• Stimulants (methylphenidate) for attention deficits
• Antidepressants (bupropion) that may also support cognition
• Medications targeting specific underlying conditions
• Supplements supporting cognitive function (though evidence varies)

Emerging Therapies

Several innovative approaches are being researched:

• Non-invasive brain stimulation
• Hyperbaric oxygen therapy
• Targeted anti-inflammatory treatments
• Cognitive rehabilitation programs

Living With Brain Fog: Practical Strategies

While working on addressing the root causes, several strategies can help manage daily challenges:

Cognitive Accommodations

• Single-tasking: Focus on one task at a time rather than multitasking
• Written reminders: Use apps, calendars, and notes extensively
• Structured routines: Establish consistent patterns to reduce cognitive load
• Environmental modifications: Minimise distractions in your workspace
• Energy management: Schedule cognitively demanding tasks during your best times of day

Communication Strategies

• Be open with employers, family, and friends about your cognitive challenges
• Request accommodations at work if needed
• Use tools like emails to follow up on verbal conversations
• Give yourself permission to ask for repetition or clarification

Self-Compassion

• Recognise that brain fog is a real symptom with biological underpinnings
• Avoid self-criticism for cognitive difficulties
• Celebrate small victories and improvements
• Connect with others experiencing similar challenges

When to See a Doctor About Brain Fog

While occasional mental cloudiness is normal, certain situations warrant medical evaluation:

Seek medical attention if:

• It is persistent (lasting weeks to months)
• Symptoms are worsening over time
• Cognitive difficulties significantly impact work or daily activities
• Brain fog is accompanied by other concerning symptoms (severe headache, weakness, vision changes, etc.)
• You’re experiencing mood changes or thoughts of self-harm
• It began suddenly or after a specific event (infection, injury, medication change)

What to tell your doctor:

• When symptoms started
• Pattern and severity of symptoms
• Impact on daily functioning
• Associated symptoms
• Potential triggers or relieving factors
• Your concerns and goals for treatment

The Future of Brain Fog Research and Treatment

Brain fog research is expanding rapidly, driven partly by the long COVID pandemic’s spotlight on persistent cognitive symptoms. Several promising directions include:

Better Characterisation

Researchers are working to:

• Develop standardised definitions and measurement tools
• Understand transdiagnostic commonalities and differences
• Identify specific subtypes or phenotypes of brain fog
• Clarify the relationship between subjective symptoms and objective performance

Mechanistic Understanding

Ongoing research is investigating:

• Specific neurobiological pathways underlying brain fog
• The role of neuroinflammation and immune dysregulation
• Contributions of vascular and metabolic factors
• Genetic and epigenetic influences
• The gut-brain axis and microbiome’s role in cognitive symptoms

Novel Treatments

Emerging therapeutic approaches include:

• Precision medicine targeting specific mechanisms
• Biomarker-guided treatment selection
• Digital cognitive interventions
• Neuromodulation techniques
• Gut microbiome-targeted therapies

Transdiagnostic Approaches

Recognition that brain fog appears similar across multiple conditions is driving research into common mechanisms and treatments that could benefit diverse patient populations.

Conclusion: Understanding Brain Fog Is the First Step

It is more than just occasional forgetfulness—it’s a genuine phenomenon affecting millions of people worldwide. Characterised by difficulty concentrating, slowed thinking, memory problems, and mental fatigue, brain fog significantly impacts quality of life, work performance, and psychological wellbeing.

While it is associated with numerous medical conditions—from long COVID to menopause to autoimmune disorders—the experience is remarkably similar across these conditions. This suggests potential common mechanisms and therapeutic targets, particularly the emerging recognition of the gut-brain connection in cognitive function.

Understanding brain fog is crucial because:

1. Validation: Recognising it as a real symptom helps people seek appropriate help
2. Direction: Identifying potential causes guides effective treatment
3. Hope: Many causes of it are treatable or manageable
4. Action: Understanding enables informed decisions about testing and interventions

If you’re experiencing persistent brain fog, remember that you’re not alone, and you’re not “going crazy.” These cognitive difficulties have biological underpinnings that can often be identified and addressed.

Take the Next Step

Understanding this symptom starts with understanding your body’s internal environment. Since gut health plays a crucial role in cognitive function, assessing your microbiome and digestive health can provide valuable insights into potential contributing factors.

Discover the reasons for your gut symptoms.

View our gut health tests

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Disclaimer: This blog is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before making decisions about your health or treatment.