18 Causes of Brain Fog

We all likely have experienced "brain fog"—the sluggish, cloudy feeling you get in your head when you can't focus, feel exhausted but cannot sleep, forget things, or make simple mistakes. Brain fog causes may include a lack of sleep, hormonal changes, or several health conditions—such as anxiety, COVID-19, fibromyalgia, and Lyme disease.

Brain fog exists on a spectrum. For some, it's a frustrating—even debilitating—everyday part of life. There may be an underlying cause if your brain fog is persistent, getting in the way of your day-to-day life and negatively affecting your mental health.

Read on to learn about 18 brain fog causes, how to deal with cognitive difficulties, and when to see a healthcare provider.

What Is Brain Fog? 

"Brain fog" is a colloquial term that describes cognitive difficulties.

Physician Georg Greiner was one of the first to use "brain fog" in the 1800s to describe delirium, a mental state that causes an inability to think clearly. Over time, people have used "brain fog" to explain mental lethargy that often accompanies several health conditions. 

Research has found that inflammation in the brain triggers brain fog. The nerve cells in different regions of your brain send signals to each other to communicate and help you focus, perform tasks, and think clearly. Inflammation in your brain damages those nerve cells, making it hard for them to transmit signals.

Brain fog symptoms may include:

• Feeling mentally "fuzzy"
• Inability to think clearly
• Lack of mental clarity
• Memory problems
• Spacing out
• Trouble concentrating

1. ADHD

Attention deficit hyperactivity disorder (ADHD) is a mental disorder that typically begins during childhood or adolescence.

ADHD causes symptoms like:

• An inability to focus
• Overactive behavior
• Trouble controlling behavior

Some people with ADHD may have symptoms that resemble brain fog, such as forgetfulness or trouble focusing. A study published in 2014 found that people with ADHD often self-reported cognitive difficulties such as memory problems and trouble with executive functioning (i.e., following instructions, multitasking, and planning).

ADHD treatment usually involves a combination of behavioral therapy, which helps manage behavior and medication.

2. Allergies

Hay fever is an allergic reaction to pollen from grasses, trees, and weeds, generally during the spring, summer, and fall. Hay fever symptoms typically include a runny or stuffy nose and sneezing.

Some evidence suggests that some people with hay fever report brain fog-related symptoms like memory problems and trouble concentrating. A study published in 2021 noted that exposure to pollen may alter brain function, causing high anxiety levels, which may cause brain fog.

Medicines, nasal irrigation with saline, and nasal sprays help treat hay fever symptoms. Allergy shots help decrease your sensitivity to pollen.

3. Cancer

Brain fog is a common side effect of cancer treatments. People often refer to cognitive difficulties during cancer treatment as "chemo brain." People with chemo brain may notice difficulty finding the right words, spacing out, or trouble recalling memories.

Cancer, or abnormal and uncontrolled cell growth, can affect nearly every tissue, such as breast, bone, and skin. Treating cancer depends on the type and its stage but typically includes chemotherapy, radiation, and surgery, among other treatments. Chemotherapy typically causes chemo brain, though other treatments may also cause brain fog.

A healthcare provider may advise cognitive rehabilitation, exercise, and meditation to help manage chemo brain. Cognitive rehabilitation involves activities like doing word puzzles or using a planner to improve brain function.

4. Celiac Disease and Gluten Sensitivity

Celiac disease causes the immune system to attack the small intestine when you eat gluten, a protein in wheat and other grains.

Celiac disease causes an array of gut-related symptoms like:

• Abdominal pain
• Bloating
• Constipation
• Diarrhea

Other symptoms, like fatigue, joint pain, or mouth sores, can occur, and some may affect your brain. People with celiac-related brain fog report feeling disoriented, forgetful, and unable to focus or pay attention. Research has found that people with celiac disease who follow a strict gluten-free diet have improved cognitive performance.

5. Chronic Fatigue Syndrome

Chronic fatigue syndrome (CFS)—also known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)—causes cognitive and physical fatigue that lasts more than six months. Rest often does not improve CFS.

Researchers do not know the cause of CFS. Still, some evidence suggests that widespread inflammation in the brain may be the culprit. As a result, people with CFS often have brain fog symptoms like difficulty concentrating and sluggish thinking.

There's no cure for CFS, but a healthcare provider can advise treatments to manage your symptoms like brain fog. Medicines, such as antidepressants, and therapy help alleviate CFS symptoms. Treatments like massage, meditation, and yoga may also help improve brain fog.

6. Cirrhosis

Cirrhosis is a chronic disease that causes scar tissue to form in your liver. Some of the most common causes of cirrhosis include heavy alcohol use and hepatitis C. People with cirrhosis may develop hepatic encephalopathy (HE), a nervous system disorder with cognitive effects.

"HE happens when the body builds up ammonia because the liver is not doing a good job metabolizing it," Tamar Taddei, MD, a professor of internal medicine at the Yale School of Medicine, told Health. "[Ammonia] can go to the brain and cause what you could call brain fog."

HE is a severe condition that may lead to coma, said Dr. Taddei. Talk to a healthcare provider about a treatment plan if you have cirrhosis. They may advise that you avoid or limit alcohol use. You may require a liver transplant if you have significant scar tissue in your liver.

7. COVID-19

Brain fog is a commonly reported symptom of long COVID, or symptoms that occur after COVID-19 infection and last longer than 28 days. Some evidence suggests that nearly one-third of people had cognitive difficulties for weeks or months after COVID-19 infection.

Anyone can develop long COVID, though risk generally increases with COVID-19 symptoms severity. Vaccination helps decrease your risk of severe illness and, possibly, long COVID. Antiviral medicines, like Paxlovid (nirmatrelvir with ritonavir), help treat COVID-19 symptoms severity if you get sick.

8. Fibromyalgia

Fibromyalgia is a chronic disorder that causes widespread pain and fatigue. Fibromyalgia affects about 2% of adults in the United States and typically affects more women than men.

People with fibromyalgia may experience brain fog, sometimes called "fibro fog," which includes difficulty concentrating and thinking and memory problems. Research has found that painful symptoms make sleeping difficult and increase fatigue, which may worsen brain fog.

Fibromyalgia treatment typically includes lifestyle changes, medicine, and therapy. Eating a healthy diet, getting enough sleep, reducing stress, and regularly exercising may help alleviate fibro fog.

9. Hormonal Changes 

Changes in hormones, such as during periods, pregnancy, and menopause, may cause cognitive difficulties.

Brain fog, also known as "period brain," may be a premenstrual syndrome (PMS) symptom. Changing amounts of estrogen and progesterone throughout your menstrual cycle may affect cognitive function. Research has found that some people have difficulty concentrating after ovulation and before their period begins.

You may have heard the term "pregnancy brain" when referring to the brain fog that some pregnant people have. A study published in 2014 found that pregnant and postpartum people commonly self-report memory difficulties.

Menopause occurs 12 months after your last period, typically during your 40s or 50s. Research has found that menopausal people often report feeling forgetful and having difficulty concentrating.

10. Kidney Failure

Kidney failure happens if something damages your kidneys, causing excess fluids and waste in your body. You will require dialysis or a kidney transplant if you have kidney failure to help your kidneys function normally.

Research has found that brain fog may be a side effect of hemodialysis, a type of kidney failure treatment. A study published in 2018 noted that harmful waste build-up and inflammation may trigger brain fog.

11. Lupus

Lupus is a chronic autoimmune disease, meaning your immune system mistakes your healthy cells as invaders and attacks them. As a result, lupus causes inflammation and pain. Systemic lupus erythematosus (SLE), one of the most common forms of lupus, affects 200,000 adults in the United States.

Lupus may cause brain fog, also known as "lupus fog," which may lead to symptoms like:

• Confusion
• Difficulty concentrating
• Difficulty keeping a schedule or remembering names
• Lapses in memory
• Problems with processing thoughts
• Trouble completing familiar tasks

Lupus-related brain fog usually ebbs and flows. In some people, brain fog may interfere significantly with daily life. 

Talk to a healthcare provider about treatments that may address your symptoms and ways to avoid memory issues. For example, you can do puzzles, read books, or use planners or color-coded calendars.

12. Lyme Disease

Lyme disease, which transmits through tick bites, often starts with the classic "bulls-eye" rash. Lyme disease can later progress into multiple symptoms, including brain fog.

Brain fog can occur anytime after infection, possibly even years after infection. Cognitive difficulties typically include memory problems and trouble concentrating. Some people with Lyme disease develop sleep disorders, which may lead to a lack of sleep that worsens brain fog.

Seek medical help right away if you have brain fog and bulls-eye rash or know a tick has bitten you. Early treatment with antibiotics helps treat Lyme disease.

13. Migraines

Migraine is a severely debilitating health condition, with symptoms ranging from intense head pain to fatigue, nausea, and vomiting. Those symptoms can create a foggy feeling in your brain.

Brain fog may be part of what some people call a "migraine hangover," or "postdrome," in the hours or days after a migraine. One of the most common symptoms of postdrome is difficulty concentrating. Other symptoms may include a stiff neck and tiredness.

There's no cure for migraine. Avoiding triggers like anxiety, bright lights, and caffeine may help reduce the frequency of migraines. Medicines that alleviate migraine symptoms include ergotamine and triptan drugs and pain relievers.

Other migraine remedies include:

• Laying down in a dark, quiet room with your eyes shut
• Placing a cold compress on your forehead
• Staying hydrated

14. Mood Disorders 

Depression often causes a loss of interest in your favorite activities and persistent sadness. You may find your thinking and speaking slow, or you need help focusing, making decisions, and remembering things.

Anxiety is a response to stress that causes feelings of fear. Research has found that anxiety may cause brain fog-related symptoms like impaired memory.

The aftermath of anxiety and depression brain fog could lead to worse feelings about yourself and make it difficult to reach out for help. Still, treatment options are available. Many effective medicines and forms of therapy that treat mood disorders might help with cognitive symptoms.

15. Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease that causes lesions on the central nervous system. Those lesions often affect cognition, emotions, how you think, and motor function.

MS brain fog "commonly affects the speed at which people can process information and their ability to recall things," Kathleen Costello, RDN, associate vice president of healthcare access of the National MS Society, told Health. Brain fog may also leave you having difficulty making decisions or remembering how to do a job.

Some evidence suggests an overlap of MS with sleep disorders. Having no or restless sleep can exasperate brain fog. Heat may also trigger brain fog, said Costello.

Talk to a healthcare provider about MS treatments that help alleviate brain fog. They may advise some workaround strategies. For instance, consider creating quiet environments for working, making checklists, and using memory aids.

16. Sjögren’s Syndrome

Dry eyes and mouth are the classic symptoms of Sjögren's syndrome, a chronic inflammatory autoimmune disease. Some people with Sjögren's syndrome have brain fog that usually involves memory lapses and poor concentration.

Research has found that cognitive challenges are sometimes the first signs of Sjögren's syndrome and may result from fatigue. Still, more research is needed to understand the relationship between Sjögren's syndrome and cognitive difficulties.

Treatment depends on your symptoms but may include artificial tears to treat dry eyes. Research has found that aerobic exercises may manage fatigue in some people with Sjögren's syndrome.

17. Sleep Disorders

You may have frequent, severe brain fog if you have a sleep disorder. 

Some of the most common sleep disorders include:

• Insomnia: An inability to fall or stay asleep or both
• Narcolepsy: Excessive daytime sleepiness
• Restless legs syndrome: A "creeping" sensation that causes leg pain, particularly at night
• Sleep apnea: "Gasping," snoring, or stopping and beginning breathing while you sleep

Those sleep disorders may lead to a lack of sleep and tiredness, which causes brain fog-related symptoms like difficulty completing tasks, feeling confused, and problems with paying attention.

Treatment depends on your sleep disorder but typically involves practicing good sleep habits. For example, try waking up and going to bed at the same time every day. Avoid looking at your phone before going to sleep, and make sure your bedroom is cool, dark, and quiet.

18. Thyroid Issues

Your thyroid secretes hormones that control your body's energy. Hypothyroidism, or an underactive thyroid, may lead to depression, sluggishness, and weight gain.

Thyroid-related brain fog may cause other symptoms like:

• Confusion
• Memory issues
• Spacing out
• Trouble concentrating

Hypothyroidism can progress slowly, so you may not notice it at first and perhaps mistake brain fog for a cloudy day in your head. Over time, continuous brain fog can disrupt your daily activities. A survey published in 2022 found that people with hypothyroidism who report brain fog also had fatigue and forgetfulness.

Treatment usually involves medicine to stabilize your thyroid hormone level. A healthcare provider will likely regularly check your thyroid hormone level using a blood test and adjust your dose as needed.

Diagnosis 

Brain fog is a symptom of several health conditions, so no guidelines exist for diagnosing it. Instead, a healthcare provider may conduct a differential diagnosis to narrow down what's causing your brain fog.

Differential diagnosis is a process of ruling out health conditions that resemble your symptoms. A healthcare provider will likely order lab tests based on your health history, physical exam, and symptoms. They may conduct a mental health screening to check for mood disorders like anxiety and depression.

Tips for Dealing With Brain Fog

Some evidence suggests that treating the underlying cause of brain fog helps alleviate cognitive difficulties in three months.

Other lifestyle changes and therapies that may help you deal with brain fog include:

• Cognitive behavioral therapy (CBT): This type of therapy helps you cope with anxiety and depression, which may cause brain fog. 
• Diet: An anti-inflammatory diet may alleviate brain fog symptoms by reducing inflammation in the brain. For example, the Mediterranean diet includes primarily plant-based foods, lean meat, and whole grains, limiting red meat and sweets. The Mediterranean diet may decrease inflammation and provide your body's essential nutrients.
• Exercise: Regular physical activity supports mental functioning by supplying oxygen to your brain, which strengthens communication between nerve cells. The Centers for Disease Control and Prevention advises exercising 150 minutes per week (e.g., 30 minutes daily, five days per week).
• Occupational therapy: This type of therapy helps people with cognitive, physical, or sensory barriers. For example, occupational therapy may help you cope with MS, which may cause brain fog.
• Sleep: A lack of sleep may cause or worsen brain fog. Adults need seven to eight hours of sleep nightly to support mental and physical functioning.

When To Contact a Healthcare Provider

Many people often have brief instances of brain fog, or moments when they have trouble finding the right words, focusing, and remembering things. Those moments usually do not last very long. You might consult a healthcare provider if cognitive difficulties persist for several weeks or longer and impact your daily activities.

Brain fog may be a sign or symptom of several health conditions. Keep track of your symptoms, including when they started, to share with a healthcare provider. Note what triggers your brain fog and what helps resolve it.

A Quick Review

Brain fog can come with overexertion, poor sleep, and stress. Persistent brain fog may be a sign or symptom of a health condition, like anxiety, COVID-19, fibromyalgia, and Lyme disease.

Consult a healthcare provider if you develop brain fog that does not go away and interferes with your daily activities. A healthy diet, exercise, and sleep typically help alleviate brain fog. Other treatments may include CBT or occupational therapy, in which you learn ways to manage cognitive difficulties.