You lose track
You forget what you were saying or what you went into a room to do.
What Is Brain Fog?
Brain fog means you have trouble concentrating, remembering, finding words or thinking as clearly as usual. It describes your symptoms, not their cause. For some people it comes and goes; others struggle with it every day.
What does brain fog feel like?
Brain fog can feel like a phone at 5% battery. You might feel okay in the morning, then struggle to think clearly by the afternoon.
You need more time
Familiar questions take longer to answer. Learning something new or solving a problem takes more effort than it used to.
You struggle to concentrate
You read the same sentence again because you didn't take it in.
You can't find the word
You know what you mean but can't remember the word you want.
You get overwhelmed
You struggle to follow a conversation when several people talk at once.
You struggle with tasks
You know a message needs an answer. You type a few words, delete them, put the phone down, pick it up again, and it is still unanswered. Other tasks can be hard to finish because you lose track of the steps.
You get through one task, then can’t do anything else
The appointment is done. You got home. Hours later, the laundry waits and the evening is gone.
You want to join in, but can’t think of what to say
The conversation is happening. You should be able to reply. Instead you go quiet and hope nobody asks what's wrong.
You put in extra work so nobody notices you’re struggling
You keep notes open, prepare more than usual, hold back from speaking too soon, and hope nobody notices the gap between hearing something and being able to use it.
You keep checking because you don’t trust your memory
You hover over the message before sending it. You ask, did I already say that? You check the time again. Other people may not notice your brain fog. You live with the doubt.
Other people can mistake late replies for not caring, silence for moodiness and forgetting for disrespect.
People also call it mental fog or brain fatigue. If you're forgetting familiar information, getting steadily worse or other people notice changes before you do, arrange a medical assessment.
What can cause brain fog?
Poor sleep, illness, hormone changes and some medications can cause brain fog. Look at when it started, what makes it worse and any other symptoms you have.
Sleep apnea
You wake up tired despite spending enough time in bed. Snoring, gasping or repeatedly waking during the night are reasons to check your sleep.
Sleep apneaADHD
You struggle to start tasks, switch between them or remember the steps. A boring task can be hard to start even when you can work quickly under pressure. Poor sleep and a lack of routine can make this worse.
ADHDMenopause
Trouble concentrating or finding words can appear alongside hot flashes and disrupted sleep around menopause.
MenopausePOTS
Thinking gets harder when you stand, spend time in the heat or take a shower, and improves when you lie down. You may also feel dizzy or notice your heart racing.
POTSMigraine
Light, sound, motion or screens may bother you alongside nausea, neck tension and trouble thinking. A migraine doesn't always include a strong headache.
MigraineLong COVID and ME/CFS
You may feel fine during physical or mental activity, then feel worse hours later or the next day. That can include more trouble concentrating, finding words or managing everyday tasks.
Long COVID and ME/CFSMedication effects
Brain fog may start after you begin a medication or change its dose or timing. Ask about medicines that make you sleepy and whether several of your medicines could be affecting your memory together.
Medication effectsDepression
Thinking and remembering can take more effort alongside a loss of interest, motivation or enjoyment. Sadness isn't always the first thing you notice.
DepressionAn underactive thyroid
Memory and concentration problems can come with tiredness, feeling cold, constipation, dry skin, hair loss or weight changes.
Thyroid problemsConcussion
After a head injury, screens, noise or mental effort can bring on symptoms that weren't a problem before.
Post-concussion symptomsLupus and autoimmune conditions
Thinking difficulties may worsen alongside other symptoms during a flare. Fatigue, pain, poor sleep, mood changes, anemia and medication effects can also affect how clearly you think.
LupusPTSD
Feeling constantly watchful or detached can interrupt concentration and memory. You may go blank, struggle to find words or feel numb after stress.
PTSDYou can have more than one cause. ADHD and sleep apnea can occur together, as can thyroid problems and anemia. Long COVID can overlap with POTS. Treating one problem may help while another still needs attention.
What studies have found about brain fog
Some studies ask people about brain fog. Others test attention, memory, processing speed, fatigue, or daily functioning.
Brain fog can affect more than your memory
A 2025 cross-condition review describes brain fog as overlapping symptoms involving thinking, fatigue, and mood.
You can struggle even when your test results are normal
Some studies find measurable changes in thinking. Others find that fatigue, depression, body symptoms, and how people feel can matter even when one screening test looks normal.
People mean different things by “brain fog”
It gives patients a way to name the problem. But researchers warn it can lump together attention, memory, language, fatigue, mood, and daily function. Work out which part gives you the most trouble.
Which tests and treatments can help?
Tests can find some causes of brain fog, but no single test checks for all of them.
Blood tests can identify problems such as anemia, thyroid disease or abnormal blood sugar. A sleep study checks for problems such as sleep apnea. Brain scans look for structural changes. These tests answer different questions, so which ones are useful depends on your symptoms and history.
A short memory test in a quiet room may miss the problems you have during a full workday, in a busy place, while standing or after activity. A normal score doesn't mean those difficulties aren't happening.
Treatment depends on what is causing the problem. Treating sleep apnea is different from treating a migraine or reviewing a medication's side effects.
What can you try next?
Try a Quick Win for practical changes you can make today and why they might help.
Take the quiz to explore possible causes based on your symptoms and health.
Already suspect a cause? Open its guide above for symptoms, tests and treatment options.
Symptoms aren't going away? Write down when they started, what else changed and what you've already had checked. Use this to prepare for an appointment.
How long does recovery take? Some symptoms improve quickly; others take longer or come and go. See what affects recovery.
Get urgent help for sudden or rapidly worsening confusion, trouble speaking, one-sided weakness, vision changes, a seizure, an unusually severe headache, or fever with a stiff neck. New thinking difficulties after a head injury also need prompt assessment.
Numbers and sources
In 2024, 17.8% of US adults aged 18 to 39 reported serious difficulty concentrating, remembering or making decisions, up from 10.0% in 2013. That represents 16.2 million people. Among people without depression, the rate rose from 5.1% to 9.8%. The survey measured cognitive disability, not a brain fog diagnosis. Read the study.
A 2026 review found brain fog in 30% of people with Long COVID. That figure applies to people with Long COVID, not the whole population. Read the review.
Denno et al., 2025: defining brain fog across conditions. Alim-Marvasti et al., 2024: subjective brain fog and daily functioning. de Havenon et al., 2026: cognitive disability among US adults aged 18 to 39, 2013 to 2024. Sanger et al., 2025: PTSD and brain fog. Elliott et al., 2026: Parkinson's disease model. Faseeh et al., 2026: Long COVID systematic review. Matthews et al., 2026: neurological effects of SARS-CoV-2. Yale Medicine, 2024: CDC Long COVID context. Maki and Jaff, 2024: menopause counseling. Tavee, 2024: Long COVID brain fog and POTS. Patel and Chong, 2021: sleep apnea cognitive outcomes. Samuels and Bernstein, 2022: hypothyroid brain fog. Sloan et al., 2025: neuropsychiatric symptoms in SLE. Drug safety review, 2025: drug-induced cognitive impairment.