The four main causes of sick building syndrome (SBS) are inadequate ventilation, indoor chemical contaminants, outdoor chemical contaminants that enter the building, and biological contaminants like mold and bacteria. These categories, identified by the EPA, often overlap. A building with poor airflow and a hidden mold problem, for example, will produce worse symptoms than either issue alone.
SBS describes a pattern where building occupants develop headaches, eye irritation, fatigue, dizziness, or respiratory discomfort that improves after they leave the building. No single illness or toxin can be pinpointed as the cause. Instead, these four broad categories interact to create an indoor environment that makes people feel sick.
1. Inadequate Ventilation
Poor ventilation is considered the single most important factor in sick building syndrome. When a building doesn’t bring in enough fresh outdoor air or doesn’t distribute it effectively, pollutants from every other source accumulate instead of being diluted and flushed out.
The history here is telling. In the early 1900s, building codes called for about 15 cubic feet per minute (cfm) of outdoor air per occupant. After the 1973 oil embargo, energy conservation measures slashed that to just 5 cfm per person. Buildings became tighter and more energy-efficient, but the air inside them grew stale. Many of the SBS complaints that emerged in the following decades traced back to this reduction.
Current ventilation standards have tried to correct this. Modern guidelines for office spaces set the baseline at 5 cfm per person plus an additional rate based on floor area, which together bring fresh air levels closer to where they were before the energy crisis. But meeting the standard on paper doesn’t always mean it works in practice. HVAC systems that are poorly maintained, improperly balanced, or undersized for actual occupancy can still leave pockets of a building with sluggish, recirculated air. If you notice your symptoms are worse in certain rooms or on certain floors, uneven air distribution is a likely contributor.
2. Indoor Chemical Contaminants
Buildings are full of materials that release volatile organic compounds (VOCs), gases that evaporate from solids and liquids at room temperature. The sources are everywhere: adhesives, carpeting, upholstery, manufactured wood products like particleboard, paints, cleaning agents, and even office equipment like copiers and printers. Correction fluid, permanent markers, and carbonless copy paper also contribute. In most cases no single product is dangerous on its own, but the cumulative load of dozens of low-level sources in a sealed indoor space can become significant.
New or recently renovated buildings tend to have the highest VOC levels because fresh materials off-gas most intensely in the first weeks and months. This is why SBS complaints often spike after a renovation or a move into a new space. Concentrations decrease over time, but they never fully disappear as long as the source materials remain. Sealing exposed surfaces of paneling and furnishings can reduce off-gassing when removing the source isn’t practical. Proper ventilation dilutes what’s left, which is why this cause and the first one are so tightly linked.
3. Outdoor Chemical Contaminants
Not all pollutants originate inside the building. Motor vehicle exhaust, construction dust, and other outdoor particulates can be pulled indoors through air intakes, windows, doors, and gaps in the building envelope. The location of a building’s air intake vents matters enormously. If they sit near a loading dock, a parking garage entrance, or a busy street, the “fresh” air the ventilation system brings in is already contaminated.
Research on urban buildings has found that placing air intakes on roof sections as far as possible from street-level channels significantly reduces the amount of traffic-related pollution drawn inside. Plumbing vents and exhaust stacks from neighboring buildings can also feed pollutants into an intake that’s poorly positioned. In dense urban areas, this cause can be particularly stubborn because the building can’t control what happens outside its walls. The fix often requires either relocating intake vents, adding high-quality filtration, or both.
4. Biological Contaminants
Mold, bacteria, viruses, dust mites, pollen, and pest-related allergens (droppings, body fragments from cockroaches and rodents) all fall into this category. These biological agents thrive wherever moisture collects: poorly ventilated bathrooms, stagnant water in HVAC drain pans, damp ceiling tiles, and water-damaged walls.
One especially serious example is Legionella bacteria, which can colonize hot water heaters, storage tanks, cooling towers, decorative fountains, and hot tubs within a building’s water system. Legionella causes a severe form of pneumonia, so its presence crosses the line from SBS into a diagnosable building-related illness. For the more common biological contaminants, the strategy is controlling moisture at the source, maintaining HVAC systems so they don’t become breeding grounds, and using appropriate air filtration. A building with chronically high humidity or visible water staining is a building that likely has a biological contamination problem, even if no one has tested for it yet.
Why These Causes Often Act Together
In practice, sick building syndrome rarely comes from a single cause. A building with poor ventilation concentrates both the VOCs from new carpet and the mold spores from a leaky pipe. An office near a highway pulls in exhaust through its HVAC system, which also happens to have standing water in the drain pan growing bacteria. The overlapping nature of these causes is one reason SBS can be so difficult to pin down and so frustrating for the people experiencing it.
Workplace stress and environmental discomfort also amplify the picture. Research from Cornell University involving nearly 4,500 office workers found that job stress, job dissatisfaction, poor lighting, and excessive noise all significantly increased the number of SBS symptoms people reported, independent of air quality. Stress appears to lower the body’s tolerance for environmental irritants, meaning the same air quality that one person shrugs off can produce real symptoms in someone under heavy work pressure. This doesn’t mean the symptoms are imaginary. It means the body’s stress response and its reaction to indoor pollutants feed off each other.
How to Tell If Your Building Is the Problem
The hallmark of SBS is that symptoms develop while you’re in the building and improve after you leave. If multiple people in the same space report headaches, throat irritation, difficulty concentrating, or unusual fatigue, and those complaints ease on weekends or vacations, the building environment is the most likely explanation.
Start by noting which areas of the building feel stuffiest or have visible signs of moisture damage. Check whether air vents are blocked by furniture or partitions. Ask your facilities team when the HVAC filters were last changed and whether outdoor air dampers are functioning. If the space was recently renovated, high VOC levels from new materials are a strong possibility. Simple interventions like increasing outdoor air intake, replacing water-stained ceiling tiles, and relocating printers out of occupied work areas can sometimes resolve symptoms quickly. When they don’t, a professional indoor air quality assessment can measure ventilation rates, VOC concentrations, humidity levels, and microbial contamination to identify the specific combination of causes at play.