Skip to main content
WBF What is
brain fog?
Support WBF Take quiz

Doctor appointment handout

Updated and source checked

What to tell your doctor about air quality and brain fog

Show where symptoms happen, how fast they change, and whether anyone else in the same place feels unwell.

Start here The room, building, smoke event or appliance, and what you felt there. Bring Bring a place-by-place timeline and several time-stamped readings, if you have them. Ask What needs a medical check, and what needs a building or workplace check? Know Repeated readings can show when CO2 or particles change. They do not tell you why you feel foggy.

Appointment image

Your handout is ready.

This image shows only the appointment summary.

Air Quality and Brain Fog: What to Tell Your Doctor, a doctor appointment handout from What Is Brain Fog.
Download image
Jump to a section

What to explain

Start by telling the doctor why you are concerned.

I think air quality may be affecting my brain fog and some of my other symptoms, and I would like help looking into it. Could we review whether carbon monoxide, smoke, fine particles, poor ventilation, dampness, mold, or another exposure might be involved? Could we also discuss how an exposure might affect my breathing, sleep, thinking, or other parts of my health? Which medical or building checks may help, and could another health problem be causing the symptoms?

Questions to take in

Ask what needs a medical check and what needs a building check.

  1. Do my symptoms and timing need an urgent carbon monoxide check?
  2. Could asthma, allergy, migraine, a sleep problem, a medicine, or another health problem explain this better?
  3. Would a carbon monoxide blood test still be useful given when I left the place?
  4. Which monitor readings are useful, and which could be misleading?
  5. Does this need a medical specialist, a building inspection, occupational health, my employer, my landlord, or local public health?
  6. What symptoms should make me leave the place or seek urgent care?

Readings and tests your doctor may consider

Use each reading or test to answer one clear question.

A carbon dioxide monitor can show whether ventilation may be poor. A PM2.5 monitor can measure fine particles. A blood test may help after a recent possible carbon monoxide exposure. Breathing symptoms may need an asthma or lung assessment. A building inspection looks for sources that a medical test cannot find.

Environmental air quality review

Reviews the building, room, smoke, fuel-burning appliance, renovation, dampness, odors, and other possible sources.

Read the test guide

Indoor CO2 monitor

Shows whether ventilation may be poor. It does not identify every pollutant or prove what caused a symptom.

Read the test guide

PM2.5 monitor

Shows fine particle levels from sources such as smoke, traffic, cooking, and dust. It does not identify the source by itself.

Read the test guide

Carbon monoxide exposure review

Checks whether the timing and symptoms could fit carbon monoxide exposure.

Ask your doctor

Carboxyhemoglobin blood test when a recent carbon monoxide exposure is possible

May help after a recent suspected carbon monoxide exposure. Tell the clinician when you left the place and whether you got oxygen, because both affect what the result means.

Ask your doctor

Asthma or lung assessment when there is wheezing, cough, chest tightness, or shortness of breath

Checks breathing symptoms that may need an asthma, allergy, infection, or other lung evaluation.

Ask your doctor

Before the appointment

Bring a timeline tied to places, not only monitor screenshots.

A short timeline with the place, date, time, symptoms, and how long it took to feel better after leaving.

Several CO2, PM2.5, or outdoor air-quality readings with the time, room, head count, and whether windows were open or the ventilation on.

A note about fuel-burning heaters, stoves, fireplaces, generators, attached garages, recent smoke, renovation, dampness, mold, or strong odors.

Any carbon monoxide detector alarm, building notice, workplace report, or heating and ventilation service record.

A list of medicines, supplements, caffeine, nicotine, alcohol, and other substances.

A note if another person or pet in the same place became ill. Leave out another person's private medical details.

Record several air readings from the same place at different times.

Add the time, room, number of people, ventilation, outdoor air, and symptoms to each reading.

How the doctor assesses this

Signs the air may be part of your brain fog

  • The same place or exposure keeps coming before brain fog.
  • Symptoms improve after you leave or the air changes.
  • Headache, dizziness, nausea, breathing trouble, irritation, or illness in another person happens at the same time.

Signs another health problem may need checking

  • Brain fog is the same in every place and doesn't improve after several days away.
  • Symptoms began after a medicine change, infection, head injury, sleep problem, or another health change, not after entering the building or breathing the affected air.
  • The only evidence is one consumer monitor reading, with no repeat reading, known exposure, or change in symptoms after leaving the place.
  • The problem keeps getting worse, even in places with different air, heat, or ventilation.

What to understand before choosing care

What your doctor needs to check about the symptoms and possible exposure.

  • The same room, building, vehicle, smoke event, or appliance repeatedly comes before the symptoms.
  • Headache, dizziness, nausea, breathing trouble, eye or throat irritation, or similar illness in another person makes an exposure more important to check.

What the research found

What carbon dioxide, PM2.5, and air-cleaner numbers can and cannot tell you.

For workplace ventilation, UK HSE says 1,000 ppm CO2 is roughly equal to 10 litres of fresh air per second per person. Readings that stay above 1,500 ppm in an occupied room point to poor ventilation. HSE says these numbers are a broad ventilation guide, not proof that a room is medically safe.

Researchers followed 302 office workers in six countries for 12 months. They linked higher PM2.5 and higher CO2, used as a sign of lower ventilation, to slower responses or fewer correct answers in 8 of 10 test measures. Because this was an observational study, it cannot prove that either reading caused one person's brain fog.

In a 2025 experiment, 26 adults spent one hour in either high particle pollution or clean air and repeated four thinking tests four hours later. Selective attention and reading facial expressions were worse after particle exposure. Working memory and sustained attention were not. This small controlled study shows a possible short-term effect, not a personal cutoff or diagnosis.

EPA's outdoor PM2.5 standards are 9.0 micrograms per cubic metre as an annual average and 35 micrograms per cubic metre over 24 hours. These are outdoor regulatory standards based on approved monitoring methods. Write down a home sensor reading with the place, date, time, symptoms, and device name. It is not the same as an EPA monitor or an indoor medical limit.

EPA's sizing guide assumes an 8-foot ceiling. It gives a minimum smoke CADR (clean air delivery rate) of 65 cubic feet per minute for 100 square feet, 195 for 300, and 325 for 500. A correctly sized cleaner can reduce particles but can't remove every pollutant, fix a carbon monoxide source, lower CO2, or repair dampness.

How age, pregnancy, and existing health problems can change the risk from polluted air.

Children can be more affected by air pollution and may describe headache, tiredness, poor focus, cough, or feeling sick instead of naming an exposure.

Older adults and people with heart disease, lung disease, asthma, anemia, or diabetes may become ill more easily from smoke, particle pollution, or carbon monoxide.

Pregnancy can increase vulnerability to some air pollutants. Mention pregnancy when asking for medical or public-health advice.

Children, older adults, pregnant people, and people with heart or lung disease may need quicker advice about a suspected air exposure.

If several people of different ages feel ill in the same place, leave the area and check for a shared exposure such as carbon monoxide, smoke, or fumes.

If the answer is no

If your doctor will not order a broad air-quality test

One blood test or home monitor cannot answer every indoor-air question. The EPA says low-cost monitors detect only the pollutants they were built to detect. Their readings do not show whether a pollutant caused your symptoms. Your health and the building may need separate checks.

What changes the answer

  • Separate the health question from the building question. Ask which symptoms need medical care. A landlord, employer, inspector, or public health service may need to check the building.
  • Bring a place-based timeline. Record where symptoms start, whether they improve after you leave, and whether other people there are affected. Include dates and times.
  • Name the suspected source. Smoke, a fuel-burning appliance, renovation dust, dampness, and workplace chemicals need different checks. Bring details about the product, appliance, or event.
  • Ask about a focused test. A recent, named exposure may have a medical test with a short time window. If it does not, agree on symptom care and a building check.
US EPA: low-cost air pollution monitors and indoor air quality

United States, United Kingdom, and Australia

Know who handles health, housing, and workplace concerns.

US United States

Start with safety, then the symptom review. Leave immediately after a carbon monoxide alarm or shared sudden illness. For ongoing symptoms, bring the location timeline to primary care and ask who should assess the building.

  • Use AirNow for the outdoor Air Quality Index (AQI). An indoor monitor measures conditions inside the room, so an outdoor AQI cannot replace an indoor reading.
  • Leave and call emergency services after a carbon monoxide alarm or a likely poisoning. This can't wait for a routine appointment.
  • For ongoing symptoms, start with primary care. Building concerns may also need an employer, landlord, local health department, or qualified building professional.
Read the EPA guide to indoor air and ventilation
UK United Kingdom

Take symptoms to a GP and building evidence to the responsible service. Use emergency services for suspected carbon monoxide poisoning. For ongoing symptoms, take the timeline to a GP and report workplace or rental problems to the responsible authority.

  • HSE describes CO2 as a broad ventilation guide, not proof that a room is safe or unsafe.
  • Use the UK Daily Air Quality Index for outdoor pollution and follow its advice for your health group.
  • A GP or NHS 111 handles health questions. Workplace or housing concerns may also involve an employer, HSE, landlord, or local council.
Read the HSE guide to using CO2 monitors for workplace ventilation
AU Australia

Use local air advice and take persistent symptoms to a GP. Follow state or territory smoke instructions. Take your symptom and location notes to a GP, and report workplace air concerns through the relevant safety authority.

  • Follow state or territory air-quality and bushfire advice because monitoring and public-health instructions vary by location.
  • Fine particles called PM2.5 are the main health concern in bushfire smoke. A HEPA cleaner has to match the room size.
  • A GP handles ongoing symptoms. Call triple zero for severe symptoms or a suspected life-threatening exposure.
Read the Australian CDC environmental health guide

Safety

Show how it affects daily life

  • What you could not do safely in that place: work, study, drive, cook.
  • How fast symptoms start after you go in, and how fast they ease after you leave.
  • Compare the same task in the suspected place and in a different place when possible.
  • Notice whether sleep changes with where you sleep, not only how many hours you get.
  • Record breathing, eye, nose, throat, headache, nausea, dizziness, and chest symptoms alongside the brain fog.

Source checked

Sources behind this handout.

  1. Cedeño Laurent JG et al. Associations between acute exposures to PM2.5 and carbon dioxide indoors and cognitive function in office workers. Environ Res Lett. 2021;16(9):094047. PMID: 35330988.

    Source

  2. Faherty T et al. Acute particulate matter exposure diminishes executive cognitive functioning after four hours regardless of inhalation pathway. Nat Commun. 2025;16:1339. PMID: 39915448.

    DOI

  3. UK Health and Safety Executive. Using CO2 monitors to assess workplace ventilation.

    Source

  4. US Environmental Protection Agency. 2024 Revised Annual PM2.5 National Ambient Air Quality Standard.

    Source

  5. US Environmental Protection Agency. Guide to Air Cleaners in the Home. Updated 2026.

    Source

  6. Centers for Disease Control and Prevention. Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe Weather.

    Source