Sick building syndrome:
symptoms, and how
to test for it

A floor of an office where several people have persistent afternoon headaches. A staff room where everyone feels dull. A department with more sick leave than the rest of the company and no medical explanation. The complaints are vague, individually deniable, and each one has a plausible alternative cause — stress, screens, dust, the season.

The pattern that makes it a building problem rather than a collection of unrelated personal ones is temporal: the symptoms ease within hours of leaving and return on re-entry. Better on weekends. Better on leave. Back by Tuesday afternoon.

What sick building syndrome is

Sick building syndrome describes a situation where occupants of a building experience acute health and comfort effects that appear linked to time spent in the building, but where no specific illness or cause can be identified. It is a description of a pattern, not a diagnosis, and it is deliberately distinguished from building-related illness — cases with a specific identified cause and clinical findings, such as Legionnaires' disease or hypersensitivity pneumonitis.

The commonly reported symptoms cluster into a few groups:

• Neurological — headache, fatigue, difficulty concentrating, drowsiness, irritability
• Mucous-membrane — dry or itchy eyes, blocked or runny nose, sore or dry throat
• Skin — dryness, itching, occasional rash
• General — nausea, dizziness, a non-specific feeling of unwellness

Every one of these is unremarkable in isolation. The signal is in the pattern across a group of people and its correlation with the building.

What causes it

Investigations consistently identify several contributing factors, with one appearing more often than the rest:

Inadequate ventilation is the most commonly implicated factor. Insufficient outdoor air means everything generated indoors — CO₂, moisture, body odour, VOCs from furnishings and cleaning products, and whatever the building materials are off-gassing — accumulates rather than being carried away. In studies where ventilation rate was measured, lower rates were associated with higher symptom prevalence.

Chemical contaminants from indoor sources — VOCs from adhesives, carpets, upholstery, printers and cleaning agents. Newly renovated or newly furnished spaces are a classic trigger, especially when ventilation is poor: the source term goes up while removal stays low.

Chemical contaminants from outdoor sources — vehicle exhaust drawn in through a badly located intake, plumbing vents, exhaust re-entrained through a nearby air inlet.

Biological contaminants — mould in damp ducts, drain pans or water-damaged material; bacteria in standing water. In Indian buildings, monsoon damp in AHU rooms and ducting is a frequent contributor.

These are not independent. Poor ventilation makes every other category worse, because dilution is the mechanism that keeps all of them tolerable. That is why it shows up so often, and why it is the sensible place to start looking.

The test

Full indoor-air investigations are expensive and slow. Before commissioning one, there is a cheap test that will either implicate ventilation or largely exclude it, and it requires one CO₂ logger and a week.

Log CO₂ continuously in the affected area for five working days. Then look at the shape of the curve:

That last row is as valuable as the others. A building whose CO₂ stays low all day is being genuinely well ventilated, which means the symptoms are coming from somewhere else — and you have just eliminated the largest and most expensive category of investigation for the price of one week of logging.

The Indian version of the problem

Several factors make this pattern especially common in Indian commercial buildings:

• Fresh-air units switched off to save electricity. Extremely common, entirely undocumented, and it converts a compliant building into a sealed box overnight. Nobody notices, because there is no display anywhere showing that it happened.
• Occupancy well above design. A floor designed for 60 people holding 100 has 40% less outdoor air per person than intended, whatever the AHU is doing.
• Sealed envelopes. Buildings are built airtight against heat, dust and noise, so there is no incidental infiltration to compensate.
• Monsoon damp in ducting. A biological contributor that peaks seasonally, and is often what makes a marginal building tip into complaints in July and August.
• Nobody measuring anything. The reason all of the above can persist for years.

Fixing it

If the CO₂ log implicates ventilation, the fix is usually much cheaper than expected, because in the great majority of cases the equipment is already installed and simply is not running when it should be.

1. Verify the fresh-air path exists and is open. Fans running, dampers not shut, intakes not blocked. This alone resolves a surprising share of cases.
2. Put the ventilation under CO₂ control. Not a timer — a timer is what produced the sawtooth. Demand control runs the fan when the space needs air and stops it when it does not, which also answers the energy objection that got the fan switched off in the first place.
3. Keep logging. The reason problems recur is that the fix is invisible. A dashboard showing a flat 700 ppm across the floor is the evidence that it is still working, six months later.
4. Then look at the rest. With ventilation confirmed adequate, remaining complaints point somewhere specific — VOCs, damp, lighting, thermal comfort — and are much easier to investigate.