Sick Building Syndrome: Why Your Office Air Feels Bad

Quick answer: Sick building syndrome describes a pattern in which people get headaches, fatigue, a stuffy nose, or eye and throat irritation that are tied to time spent in a particular building and ease within hours of leaving it. The term is widely recognized, though researchers still debate its causes. The most common factor is poor ventilation (too little outdoor air coming in), followed by pollution sources inside the building and poorly maintained HVAC systems. The defining feature is the pattern, not a single diagnosis.

The pattern that defines it

You may already know the experience: a dull headache that builds through the afternoon, heavy eyes, a dry throat, trouble focusing by 3 p.m. Then Saturday comes and none of it happens.

That contrast is the signal. The EPA describes sick building syndrome (SBS) as situations where occupants "experience acute health and comfort effects that appear to be linked to time spent in a building," while no specific illness or cause can be identified (EPA). In practice, the pattern usually looks like this:

Several people are affected in the same building or the same part of it.
Symptoms appear or get worse during time spent in the building.
They ease within hours of leaving and often clear over a weekend or vacation.
No single cause shows up in testing.

The usual symptoms are easy to dismiss one at a time: headache, fatigue, trouble concentrating, dry or itchy eyes, a stuffy or runny nose, dry throat, skin irritation, and sometimes dizziness or nausea. None of them is dramatic, which is why a building can go years without anyone connecting them.

SBS is a recognized term, used by the EPA and occupational health agencies, but it is also debated. Some researchers question whether it is one condition or several overlapping problems, and studies disagree on how much each cause contributes. What is not in doubt is that the symptoms are real and that improving building conditions often helps.

It helps to separate SBS from a related category. Building-related illness is when doctors can diagnose a specific illness and trace it directly to something in the building, such as Legionnaires' disease from a contaminated cooling tower, a documented mold exposure, or carbon monoxide from a faulty appliance (EPA). That is more serious. If symptoms are severe, include fever, or affect breathing, treat it as a medical matter: see a doctor and involve your employer's occupational health team.

Why modern buildings are prone to it

The story starts with energy. Over the past few decades, buildings became much more airtight to cut heating and cooling costs: sealed windows, tighter walls, and mechanical ventilation in place of the drafts older buildings had by accident. That saved energy. It also meant the building now depends on its ventilation system to bring in fresh air. When that system is undersized, poorly balanced, or turned down to save money, there is no backup.

The EPA's own history shows how this happened. Mid-1900s codes called for about 15 cubic feet per minute (cfm) of outdoor air per person. After the 1973 oil embargo, that was cut to 5 cfm per person to save energy, and the EPA links reduced ventilation like this to many SBS complaints. Later ASHRAE guidance raised the minimum again, to 15 cfm per person and 20 cfm per person in offices (EPA).

Add modern office contents (synthetic carpet and furniture, printers, cleaning products, scented dispensers, and many people in a small space), and you have a sealed box collecting everything produced inside it.

Cause 1: Poor ventilation

The EPA lists inadequate ventilation first among the causes of SBS, and it makes every other cause worse. When too little outdoor air comes in, everything produced indoors builds up through the day: carbon dioxide from breathing, VOCs (volatile organic compounds) from materials, odors, airborne microbes, and moisture.

The easiest way to check is carbon dioxide (CO2), because people breathe it out constantly and it is simple to measure. The bands below are common rules of thumb used by building professionals. They are not limits set by ASHRAE, whose standards specify ventilation rates rather than a CO2 ceiling (ASHRAE).

CO2 level (rule of thumb)	What it usually suggests
Under 800 ppm	Ventilation is generally keeping up
800–1,000 ppm	Acceptable; keep an eye on it
1,000–1,400 ppm	Likely under-ventilated; complaints become more common
Above 1,400 ppm	Outdoor air supply is probably falling short

At these levels, CO2 itself is not poisoning anyone. It works as a tracer. If CO2 from people's breath is building up, other things produced indoors are probably building up too. ASHRAE notes that CO2 alone doesn't tell you overall air quality, but readings far above what's expected can point to a ventilation system that isn't working properly.

A $100 to $150 CO2 monitor on your desk for a week is the most useful thing an employee can do. Choose one with an NDIR sensor (non-dispersive infrared), which measures CO2 directly.

Cause 2: Pollution sources inside the building

VOCs from new carpet, furniture, paint, adhesives, and flooring. These are strongest after a renovation, which is why complaints often start a few weeks after one.
Cleaning products and scented air fresheners, which add chemicals to the air rather than removing them.
Printers and copiers in small rooms without their own exhaust.
Poor separation from parking garages, loading docks, kitchens, or smoking areas.
Badly placed outdoor air intakes next to a loading dock, exhaust vent, or dumpster, so the "fresh" air isn't fresh.

Cause 3: The HVAC system itself

The HVAC system often gets overlooked because it is out of sight, and it is where a ventilation problem can become a biological one. Ductwork is dark, sometimes humid, and collects dust and organic debris over time. Cooling coils and drain pans hold standing water. Filters past their replacement date stop catching particles well and become a loaded, sometimes damp surface sitting in the airflow.

The result: a system meant to supply clean air can carry dust, spores, and debris from the ducts into every room it serves. A building can move plenty of air and still deliver poor air because of what the path adds along the way.

Cause 4: Humidity, too high or too low

Too high, and you get mold on cold surfaces, clammy air, and musty odors. Too low, which is common in heated offices in winter, and you get the dry eyes, dry throat, and irritated nose that make up much of the SBS symptom list. OSHA's indoor air quality guidance lists humidity among the most common office complaints (OSHA). Dry winter air can produce part of the complaint pattern on its own.

Want to measure before you escalate? See how to test indoor air quality

What you can do if you don't control the building

Most people reading this are employees, not facilities managers. You can't rebalance an air handler. You can build a clear case and take it to the right people.

Document the pattern. A documented pattern gets acted on; a vague complaint often doesn't.

Log symptoms for two weeks: date, time, where you were in the building, what you felt, and how long it took to ease after you left. Mark weekends and days off.
Ask coworkers. SBS affects groups by definition. Several people with the same time-of-day pattern carry far more weight than one person's headaches.
Measure CO2 at your desk for a week and note the daily curve. A climb from morning to mid-afternoon that resets overnight is a classic ventilation pattern.
Note building events. Did complaints start after a renovation, new carpet, a new cleaning contractor, HVAC work, or a cut in system run hours?

Raise it with specifics. Take your log and CO2 readings to your facilities manager, office manager, or safety representative, and ask three questions: When was the HVAC system last serviced and balanced? How much outdoor air is it supplying? When were the filters last changed? These questions have records behind them, which makes them hard to brush aside. OSHA's guidance tells employers that when employees raise air quality concerns, management is responsible for prompt assessment and corrective action.

If that goes nowhere, US workers have two outside options:

File a complaint with OSHA. You or a representative can file a confidential safety and health complaint online, by phone at 1-800-321-OSHA (6742), or in person, and you can file anonymously. Employers may not retaliate against you for raising a hazard (OSHA). OSHA has no general indoor air quality standard, but it does enforce rules on ventilation and specific contaminants.
Request a NIOSH Health Hazard Evaluation. The National Institute for Occupational Safety and Health (NIOSH) runs this program. Employees, union officials, or employers can ask NIOSH to evaluate possible health hazards at a workplace, and indoor environmental quality is one of the areas it investigates (NIOSH).

In the meantime, a few small steps help a little. Sit away from printers and copiers. Open a window if any open. Take breaks outside, since symptoms track time spent in the building. Skip the scented desk diffuser; it adds VOCs and muddies the pattern you're trying to document. None of these fixes the building, so keep escalating.

What fixes it at the building level

For whoever controls the building, the order of work is well established.

Priority	Action	What it addresses
1	Increase outdoor air; re-commission and balance the HVAC system	The most common cause. Nothing else makes up for too little fresh air.
2	Replace filters on schedule; use the highest rating the system can handle	Particle load; keeps loaded filters from becoming a source
3	Clean and maintain ducts, coils, and drain pans	Growth and debris in the air path
4	Remove or replace pollution sources	VOCs from materials, cleaning products, fragrance
5	Bring humidity into a comfortable range (about 30% to 60%)	Dry-air irritation at one end, mold risk at the other
6	Treat surfaces and the HVAC interior biologically	Settled organic residue that filters and airflow don't remove

Steps 1 through 5 are standard facilities practice, and in many buildings they are enough to bring complaints down. Step 6 is the one most buildings never reach.

Ventilation dilutes what is in the air, and filters capture what passes through them. Neither touches what has already settled: the organic residue on duct interiors, coils, carpet, and other surfaces. In a large building that layer is substantial, and airflow and foot traffic keep stirring it up.

That settled layer is what environmental probiotic systems are designed for. Instead of filtering air, they release beneficial Bacillus bacteria that settle on surfaces and inside ductwork and consume the organic residue that odor-causing bacteria and mold feed on. This supports a stable indoor microbiome rather than repeatedly stripping surfaces with harsh chemicals, a habit we discuss in over-sanitization. The probiotic formula is EPA registered as a bacteriostat and fungistat (EPA Reg. No. 94339-1), and it is MADE SAFE certified; the registration covers the formula, not the device.

For larger spaces, this works through the HVAC system. The E-Biotic Pro treats up to 25,000 sq ft through the existing air handling system. It is installed by certified HVAC contractors and priced by quote; facilities teams can start with our HVAC applications page.

Two limits matter. First, this adds to steps 1 through 5 and never replaces them. A building short on outdoor air is still short on outdoor air, and surface treatment doesn't change a CO2 reading. Second, it is ongoing maintenance that works over weeks. It is not a cleanup service for an identified mold problem, which needs a professional remediation contractor.

Commercial buildings are also where this technology began. Before EnviroBiotics sold home units, the company operated as BetterAir and supplied probiotic systems for commercial and institutional buildings. The story of the name change is in BetterAir to EnviroBiotics.

The bottom line

If your symptoms follow the building rather than the season, and coworkers have them too, you are not imagining it. That pattern is what sick building syndrome describes, and it usually traces back to a sealed building whose ventilation isn't keeping up. Document the pattern, measure CO2 for a week, and raise it with specifics. If internal channels stall, OSHA and NIOSH are there for US workers. At the building level, outdoor air comes first. After that come filters, maintenance, pollution sources, and humidity, with settled residue in ducts and on surfaces as the layer routine maintenance tends to miss.

Frequently asked questions

What is sick building syndrome? Sick building syndrome describes a pattern in which people in a building have symptoms such as headaches, fatigue, poor concentration, and eye, nose, or throat irritation that are linked to time spent there and ease within hours of leaving. It is defined by the pattern rather than by one identified cause, and researchers still debate its causes. When a specific illness can be traced to something in the building, such as Legionella or a documented mold exposure, it is called building-related illness instead.

What are the symptoms of sick building syndrome? The most common are headache, fatigue, trouble concentrating, dry or itchy eyes, a stuffy or runny nose, dry throat, skin irritation, and sometimes dizziness or nausea. Each one is mild and easy to blame on something else. What sets SBS apart is that several people are affected, symptoms get worse during time in the building, and they ease within hours of leaving or over a weekend.

What causes sick building syndrome? Poor ventilation is the most commonly identified factor: too little outdoor air comes in, so carbon dioxide, VOCs, odors, moisture, and airborne microbes build up during the day. Other contributors include VOCs from new carpet, furniture, and paint, poorly maintained HVAC systems with dirty ducts or overdue filters, badly placed outdoor air intakes, and humidity that is too high or too low.

How do I prove my office has poor air quality? Document the pattern. Log symptoms with date, time, and location for two weeks, note how quickly they ease after you leave, and check whether weekends are clear. Ask coworkers whether they notice the same thing. Then put a CO2 monitor at your desk for a week; a level that climbs above about 1,000 ppm through the afternoon and resets overnight is strong evidence of poor ventilation.

What CO2 level is too high in an office? As a rule of thumb, under 800 ppm suggests ventilation is keeping up, 1,000 to 1,400 ppm suggests the space is under-ventilated, and above 1,400 ppm the outdoor air supply is probably falling short. These are not official limits; ASHRAE standards set ventilation rates, not a CO2 ceiling. CO2 at these levels isn't harmful by itself, but it shows that other indoor pollutants are likely building up too.

Can air purifiers fix sick building syndrome? Not on their own. A portable air purifier captures particles in the room it sits in, which can help with dust and allergens, but it doesn't bring in outdoor air, the most common underlying problem. It also does little for VOCs unless it has a substantial activated carbon filter, and nothing for contamination inside the ductwork. Ventilation and HVAC maintenance come first.

Who is responsible for air quality in my workplace? Usually the employer and the building owner or facilities management, with specific duties that vary by state and building type. Start with your facilities manager, office manager, or safety representative, and ask for records on HVAC servicing, outdoor air supply, and filter changes. In the US, you can also file a confidential complaint with OSHA or request a NIOSH Health Hazard Evaluation.

Sick Building Syndrome: Why Your Office Air Makes You Feel Worse