Sick building syndrome (SBS) is caused by a combination of poor indoor air quality, chemical off-gassing from building materials and office equipment, biological contaminants like mold and bacteria, inadequate ventilation, and sometimes psychosocial workplace stress. Up to 30% of new and renovated buildings are estimated to have SBS problems, and prevalence among office workers ranges widely, from around 2% to over 70% depending on the building and the region studied. The symptoms, which include headaches, eye and throat irritation, fatigue, and dizziness, typically improve or disappear once a person leaves the building.
Chemical Contaminants in Indoor Air
The most common chemical culprits are volatile organic compounds (VOCs), a broad category of gases released by everyday materials found in offices and homes. Furniture, carpeting, paint, adhesives, and pressed-wood products all release VOCs as they age, a process called off-gassing that is strongest when materials are new but can continue for months or years. Formaldehyde is one of the most prevalent indoor VOCs and one of the few that can be readily measured. Office equipment adds to the load: copiers, printers, permanent markers, correction fluids, and even carbonless copy paper all emit VOCs during normal use.
The health effects of these compounds are a near-perfect match for what people in “sick” buildings report. At low concentrations typical of indoor environments, VOCs cause eye and respiratory tract irritation, headaches, dizziness, nausea, fatigue, and visual or memory problems. Some specific compounds carry greater risks. Benzene is a known human carcinogen. Methylene chloride, found in some solvents and paint strippers, gets converted to carbon monoxide inside the body, producing symptoms that mimic carbon monoxide poisoning. Perchloroethylene, a dry-cleaning chemical that can drift into adjacent spaces, has caused cancer in laboratory animals.
What makes VOC exposure particularly tricky is that concentrations of individual chemicals may each be below recognized safety limits, yet the combined cocktail of dozens of compounds can still produce symptoms. Indoor levels of many VOCs consistently measure two to five times higher than outdoor levels, even in buildings located near industrial sources.
Biological Contaminants
Mold, bacteria, pollen, and viruses thrive in buildings where moisture is poorly controlled. They breed in stagnant water that collects in air ducts, humidifiers, drain pans, ceiling tiles, carpeting, and insulation. Even insect fragments and bird droppings in ventilation systems can become airborne biological contaminants.
Inhaling mold spores is normally harmless, but in sufficient quantities it can trigger asthma, rhinitis, or bronchitis. The symptoms associated with biological contamination in buildings tend to be more respiratory in nature than those from chemical exposure: coughing, chest tightness, fever, chills, muscle aches, and upper respiratory congestion. In rare but serious cases, the bacterium Legionella can colonize building water systems and cause Legionnaire’s Disease, a severe pneumonia, or Pontiac Fever, a milder flu-like illness.
Ventilation and HVAC Problems
A building’s heating, ventilation, and air conditioning system is supposed to dilute and remove indoor pollutants by bringing in fresh outdoor air. When it fails at that job, every other cause of SBS gets worse. Dirty filters, clogged ducts, poorly maintained humidifiers, and blocked outdoor air intakes all reduce the volume of fresh air circulating through a building. That allows both chemical and biological contaminants to accumulate.
Carbon dioxide levels serve as a useful proxy for ventilation quality. In a well-ventilated building, CO2 stays around 600 parts per million (ppm). When ventilation is inadequate and occupancy is high, levels can climb to 1,000 ppm or beyond. A study from Lawrence Berkeley National Laboratory found that at 1,000 ppm, test subjects showed significant declines on six out of nine scales of decision-making performance. At 2,500 ppm, the declines were large across seven scales, with the most dramatic drops in the ability to take initiative and think strategically. These CO2 levels don’t directly cause SBS in the traditional sense, but they signal that the air exchange rate is too low, meaning everything else in the air is also building up.
Low Humidity and Physical Environment
Air quality gets most of the attention, but the physical environment matters too. Relative humidity plays a surprisingly large role. Research from Uppsala University found that when indoor humidity drops below 20 to 25%, reports of eye irritation increase substantially. Raising humidity from that range to 30 to 35% reduced SBS symptoms overall. In one longitudinal finding, SBS symptom intensity only increased in buildings where the air was not humidified, suggesting that dry air acts as a continuous low-grade irritant to the eyes and mucous membranes.
This is especially relevant in winter, when heating systems can push indoor humidity well below 20%. It’s also a factor in heavily air-conditioned buildings in hot climates. The dryness irritates the same tissues (eyes, nose, throat) that chemical and biological contaminants target, making it hard to separate from other causes without measurement.
Workplace Stress and Psychosocial Factors
Occupational stress has been consistently correlated with SBS symptoms in research, though the relationship is complicated. People under high job stress may be more sensitive to environmental irritants, or they may simply be more likely to notice and report symptoms they might otherwise tolerate. It’s also possible that the same poorly managed buildings that create air quality problems also tend to be workplaces with other quality-of-life issues.
What the research has not been able to determine is whether stress actively causes the physical symptoms or is simply present alongside them. Most studies on this question are cross-sectional, meaning they capture a snapshot rather than tracking people over time, so they can’t establish which came first. Still, the pattern is consistent enough that workplace psychosocial conditions are considered a contributing factor in most frameworks for understanding SBS.
Why It’s Rarely One Single Cause
The reason SBS is so hard to pin down in any individual building is that it almost never comes from a single source. A building might have moderate VOC levels from new carpet, slightly inadequate ventilation, low humidity from aggressive air conditioning, and a workforce under deadline pressure. None of those factors alone would cause widespread symptoms, but together they push enough people past the threshold that a pattern emerges. This is why investigators evaluating a sick building typically look at air quality, ventilation rates, moisture control, and occupant satisfaction simultaneously rather than hunting for one smoking gun.
Newly constructed or recently renovated buildings are at the highest risk because they combine peak off-gassing from new materials with HVAC systems that haven’t been fully balanced and tested. That initial period is when chemical concentrations are highest and ventilation problems are most likely to go unnoticed. The good news is that most SBS cases improve substantially once the specific combination of causes is identified: increasing fresh air supply, fixing moisture problems, removing or sealing off-gassing materials, and replacing contaminated filters or ductwork can resolve symptoms for the majority of building occupants.