What causes brain fog? Unpacking the haze

You walk into the kitchen and stand there, blank. What did you come in here for? You reread the same email three times and still cannot quite grasp what it’s saying. Mid-conversation, the perfect word hovers just out of reach. Sound familiar?

If you’ve been dismissing these moments as simply being “too tired” or “getting older”, it might be worth considering another possibility: brain fog.

Brain fog isn’t a medical diagnosis — it’s an umbrella term for a collection of cognitive symptoms that can leave you feeling mentally clouded and disconnected. While everyone has the occasional scattered moment, persistent brain fog is different. Understanding what causes it and how to address it can help you reclaim that mental clarity you’ve been missing.

What is brain fog?

Brain fog describes a state of cognitive dysfunction that makes it harder to think clearly. It’s that feeling of cloudy thinking, difficulty concentrating, and a general sense that your brain just isn’t firing on all cylinders [1].

People with brain fog often describe their thoughts as slow or fuzzy. This mental fog can be temporary or stick around for longer, depending on what’s causing it.

What are the symptoms of brain fog?

Common signs include trouble concentrating, memory problems, and finding it difficult to make decisions [1]. You might feel confused more easily or notice that everyday tasks now take considerably more time and mental energy than they used to.

Many people also experience a persistent sense of mental exhaustion that comes with brain fog [2]. This is different from feeling physically tired — you can feel mentally drained even after getting plenty of sleep. You might also find it harder to express yourself clearly, have trouble finding the right words when you’re talking or forget things soon after they've happened [1].

What causes brain fog?

The causes of brain fog are surprisingly varied — it could be a health condition, lifestyle factors, or environmental influences.

Medical conditions

Chronic fatigue syndrome: This complex condition causes extreme fatigue that doesn’t improve with rest, and often comes with cognitive difficulties too [2].

Autoimmune diseases: Conditions like multiple sclerosis, systemic lupus erythematosus, and other autoimmune disorders can affect how clearly you think [4]. These conditions cause inflammation that impacts your central nervous system and nerve cells.

Fibromyalgia: If you have fibromyalgia, you might experience “fibro fog” — memory problems and difficulty concentrating [2]. 

Hormonal changes: The menopausal transition can trigger brain fog as your hormone levels fluctuate [5]. Many women notice cognitive changes alongside hot flashes, weight gain, and sleep problems. Research suggests that around 60% of women experience some cognitive difficulties during this transition [6].

Thyroid disorders: Both an underactive and overactive thyroid can affect your thinking, often showing up as mental fog, low energy levels, and dry skin [7]. Fatigue and forgetfulness are particularly common in people with hypothyroidism [7].

Sleep disorders: Conditions like sleep apnoea or insomnia can have a significant impact on your brain health and contribute to foggy thinking [1].

Mental health conditions

There’s a strong link between mental health struggles and developing brain fog [1]. When you’re anxious, your brain is working overtime on worry, leaving less mental space for everything else [9]. It’s exhausting, and that exhaustion shows up as difficulty concentrating and fuzzy thinking.

Nutritional deficiencies

What you’re eating — or not eating — can affect how clearly you think:

Vitamin B12 deficiency: B12 is essential for your nerve cells and brain function. When you’re running low, you might notice memory issues and mental cloudiness [10].

Vitamin D deficiency: This vitamin plays a key role in brain health, and low levels have been linked to cognitive problems [6].

Iron deficiency: Without enough iron, your brain doesn’t get enough oxygen, which affects your energy and mental clarity [10].

Omega-3 fatty acids: These healthy fats are crucial for your brain to function well, and not getting enough may contribute to cognitive issues [6].

Lifestyle factors

Poor sleep, not moving your body enough, dehydration, and drinking too much alcohol can all contribute to brain fog [1]. Ongoing stress can also take its toll on your immune system and brain function over time.

How is brain fog identified?

Working out what’s causing your brain fog usually starts with a thorough chat with your healthcare provider to identify the underlying cause. There’s no single test for brain fog itself, but your clinician can run a few tests to rule out underlying conditions and work out exactly what’s going on [1].

Your provider will want to know when you notice the brain fog, how long it’s been happening, and what other symptoms you’re experiencing. They’ll probably ask about your sleep, stress levels, what you’re eating, any medications you’re taking, and your medical history.

You might need some blood tests to check for vitamin deficiencies, thyroid issues, or signs of inflammation or autoimmune conditions [7]. It can be really helpful to keep a symptom diary in the meantime. Jot down when the brain fog happens, how bad it is, anything that seems to trigger it, and how it’s affecting your day-to-day life.

Can brain fog be treated or managed?

How you manage brain fog will depend on what’s causing it in the first place. Once your clinician has figured out the root cause, they can recommend ways it can be treated or managed.

Treating underlying conditions: If your brain fog is caused by a specific medical condition, like a thyroid disorder, autoimmune disease, or sleep disorder, treating that condition will often improve your symptoms [7]. Hormone replacement therapy, for example, can help with brain fog related to menopause [5].

Nutritional support: If your blood tests show vitamin deficiencies, your healthcare provider might recommend supplements to boost your levels [10]. Adding healthy fats to your diet — like fatty fish, nuts, and avocados — also supports cognitive function.

Mental health support: When mental health conditions are contributing to your brain fog, talk therapy, stress management techniques, and certain medications can all help [9]. Cognitive behavioural therapy (CBT) with a psychologist can help address mood and anxiety issues that often accompany brain fog [5].

Lifestyle modifications: Research shows that lifestyle changes can make a real difference to brain fog [1]. Regular exercise gets more blood flowing to your brain. Getting quality sleep, staying hydrated, and managing your stress levels all play an important role, too.

Managing brain fog often requires a holistic approach that treats several factors at once.

Can brain fog be prevented?

While not all causes of brain fog are preventable, you can be proactive in your approach to supporting brain health:

• Prioritise sleep: Aim for seven to nine hours of quality sleep each night [1]. Establish a consistent sleep schedule and create a restful environment.
• Manage stress: Incorporate stress management techniques — such as mindfulness, meditation, or deep breathing exercises — into your daily routine [1].
• Stay physically active: Research suggests that moderate-intensity exercise can improve cognitive flexibility and working memory [6].
• Nourish your brain: Eat a balanced diet rich in healthy fats, antioxidants, and essential nutrients [6]. Drink plenty of water — even mild dehydration can affect how well you think.
• Limit alcohol and avoid smoking: Both can take a toll on your brain health over time [1].
• Keep your mind engaged: Learning new skills, reading, or doing puzzles keeps your mind active.
• Manage chronic conditions: If you have ongoing health issues, work with your healthcare provider to keep them well-managed.

Preventative measures work best when you stick with them consistently as part of an overall healthy lifestyle. You don’t need to overhaul everything at once — small, sustainable changes often make the biggest difference.

Lifestyle factors that may influence brain fog

Sleep quality and quantity: Poor sleep is one of the most common contributors to cognitive symptoms [1]. Sleep disorders or simply not getting enough rest can significantly affect how your brain functions.

Nutrition and hydration: A diet low in essential nutrients can leave you feeling mentally foggy, while a balanced diet supports cognitive health. Brain-friendly foods are those rich in omega-3 fatty acids, such as eggs, fish, nuts, and seeds [6]. Staying well hydrated is really important, too.

Physical movement: Regular exercise supports the immune system and can reduce inflammation throughout the body [6]. You don’t need intense physical activity — even going for regular walks can help.

Stress levels: Chronic stress takes a toll on your mental and physical health [9]. Finding effective ways to manage stress through relaxation techniques, hobbies, or talk therapy can help.

Social connections: Meaningful social interactions and maintaining a solid support network can boost cognitive health and make you feel less foggy.

Environmental factors: Your physical environment matters too. Getting enough natural light, limiting screen time, breathing fresh air, and limiting exposure to environmental toxins all help support better brain health [1].

Work-life balance: Overwork and burnout can show up as brain fog. Make sure you take plenty of short breaks, use memory aids when needed, and don’t overextend yourself.

Most people find that making gradual lifestyle changes — rather than attempting dramatic overhauls — leads to more sustainable habits long term. Focus on one or two areas at a time, and be patient with yourself.

When should you contact a healthcare provider?

While occasional mental cloudiness is normal, you should talk to your doctor in certain situations:

• Persistent symptoms: If you notice brain fog that lasts for weeks or progressively worsens [1].
• Impact on daily life: When cognitive symptoms interfere with your ability to work, maintain relationships, or complete daily tasks safely.
• Sudden onset: Seek immediate medical attention if you notice abrupt changes in your cognitive impairment, particularly if it’s accompanied by other symptoms such as severe headaches, vision changes, or difficulty speaking.
• Accompanying symptoms: If brain fog occurs alongside other concerning symptoms such as significant weight changes, persistent fatigue, mood changes, or physical symptoms[7].
• No improvement with lifestyle changes: If you’ve implemented healthy habits but continue to experience brain fog, there might be an underlying condition that needs to be addressed [7].
• Mental health concerns: If brain fog is accompanied by feelings of hopelessness, persistent anxiety, or thoughts of self-harm, please seek help immediately [9]. You can get urgent support from 111 online or by calling 111 and selecting the mental health option [11].

Remember, seeking help isn’t an overreaction. Your cognitive health is essential to your overall well-being, and healthcare providers are there to work out the cause and develop effective management strategies. You deserve to feel mentally sharp and capable.

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