SBS vs BRI vs MCS: three terms that are not interchangeable

The term "sick building syndrome" is used in casual speech to cover three things that are clinically distinct, and the conflation produces a lot of frustrated diagnostic effort. The WHO's 1983 definition still holds: SBS is a cluster of nonspecific symptoms (headache, eye and throat irritation, fatigue, difficulty concentrating) that affect a meaningful fraction of building occupants, that resolve when occupants leave the building, and for which no single specific cause has been identified. The "no identified cause" is doing a lot of work in that definition: SBS is a diagnosis of exclusion, and once a specific cause is found the case is reclassified.

BRI, building-related illness, is different in that a specific cause has been identified. Legionnaires' disease traced to a cooling tower is BRI. Hypersensitivity pneumonitis from a contaminated humidifier is BRI. Asthma exacerbation in a building with documented mold growth in the return plenum is BRI. Formaldehyde-related upper airway symptoms in a newly-built tenant space measured to have 90 ppb formaldehyde is BRI. The diagnostic path is medical and environmental in parallel: a clinician identifies the clinical syndrome, and an industrial hygienist identifies the exposure, and the two are connected by mechanism. When to call a pro describes the credentialing question; mold spores and formaldehyde cover two of the common BRI causes specifically.

MCS, multiple chemical sensitivity, is an individual-level construct, not a building-level one. It describes a person who reports symptoms triggered by low-level chemical exposures (fragrances, cleaning products, new finishes) at levels that do not produce symptoms in the general population. MCS is contested in clinical medicine, its mechanism is debated, and it is not a finding the dashboard or any environmental measurement can confirm or rule out. What we can say from the IAQ side: a building with low baseline VOC index, low PM, and good ventilation will affect a sensitive person less than one with high baseline VOC, regardless of where the sensitivity comes from biologically. The IAQ work is the same in either case; the medical interpretation is for clinicians.

How the dashboard helps disambiguate. Room-by-room patterns matter: if symptoms cluster in one wing, with elevated VOC or low ventilation in that wing, the case is moving toward BRI with a findable cause. Time-of-day patterns matter: symptoms that track HVAC startup (morning) or shutdown (evening) point at the system itself; symptoms that track cleaning crews point at cleaning products; symptoms that track a particular activity point at that activity. Multi-week ventilation correlation is what the rolling-average view is for. When the data shows nothing distinctive across rooms and time, the case stays SBS by exclusion. The honest move at that point is to improve ventilation rates per ASHRAE 62.1, lower baseline VOCs per the VOC playbook, and re-evaluate; SBS often resolves with ventilation improvement even when no specific cause is ever named. See cognitive effects of CO₂ and office IAQ for the workplace-specific framings.

This is environmental information, not medical advice. The dashboard's readings help you make decisions about the air in your space. They do not diagnose conditions, interpret symptoms, or replace conversations with your physician. If symptoms persist, worsen, or coincide with a known exposure, talk to a healthcare professional. See the AI's medical-advice scope.