Symptom · office

Brain fog at work: the sick building question

Quick answer: if your head clears on days you work elsewhere, your building earns suspicion. "Sick building syndrome" sounds mysterious; the usual mechanism is plain — not enough outdoor air per person, plus whatever the building adds (VOCs, dust, dryness).

A tired office worker rubbing their eyes at a desk — Builds over the workday, fades after you leave: the pattern that points at the building.

The pattern that points at the building

Symptoms — fog, heavy eyes, dull headache, scratchy throat — build over the workday and fade within hours of leaving. (This on-site/off-site contrast is how the EPA describes SBS.)
Multiple coworkers report the same, in the same zones.
Meeting-heavy days feel worst — see the meeting-room math.

What "better air" is worth cognitively

The Harvard COGfx study (Allen 2016) put professionals in a controlled office and dialed conditions: in the high-ventilation, low-VOC "green+" setting, cognitive scores ran dramatically higher than at conventional-office CO₂ and VOC levels — on average double versus the ~1,400 ppm condition. (And the honest caveat from the pure-CO₂ literature is on our reference page — it doesn't change what to ask your building for: more outdoor air.)

Cognitive-test scores by CO₂ condition, indexed to the high-ventilation day (=100): on average ~15% lower around ~945 ppm, ~50% lower around ~1,400 (Allen 2016 — caveats above).

What you can do from a desk

Measure at your seat. A small NDIR monitor for a week, logging. Below ~800 all day? Your fog likely isn't ventilation. Rising past 1,200 every afternoon? Now you own evidence, not a vibe.
Ask facilities two precise questions: What is the outdoor-air rate per person in my zone (ASHRAE 62.1 is the reference standard)? What MERV rating are the filters? Specific questions signal you'll understand the answers.
Claim the meeting fixes: doors open, breaks at 45 minutes, bigger rooms.
Deskside purifier? It helps with particles and dust, not CO₂ — know what it fixes before spending.

The email to facilities (copy, paste, edit)

Subject: Ventilation question — [your zone/floor]

Hi — I've been tracking CO₂ at my desk with a small NDIR monitor for [a week]. It starts near [600] each morning and climbs past [1,200–1,500] by mid-afternoon, which usually indicates the zone isn't getting much outdoor air per person. Could you tell me the design outdoor-air rate for this zone (ASHRAE 62.1 basis), and whether the economizer/outdoor-air damper is operating? Happy to share the logged data — it's a clean daily curve. Thanks for looking into it.

Why it works: it's specific, it names the standard, it offers data instead of complaint, and it asks two questions a competent facilities team can actually answer.

When it's not the building

Fog with no on-site/off-site pattern deserves the wider differential: sleep debt and apnea, low iron or B12, thyroid, depression and anxiety, medication side effects, long COVID. A pattern-free fog is a clinician conversation, not a facilities ticket.

Sources

Allen J.G. et al. (2016), EHP. doi:10.1289/ehp.1510037
US EPA — Indoor Air Facts No. 4: Sick Building Syndrome.
ASHRAE Standard 62.1 — Ventilation for Acceptable Indoor Air Quality.