Volatile organic compounds (VOCs) are carbon-based chemicals that evaporate readily at room temperature, releasing into the air ('off-gassing'). Hundreds are present in typical indoor air, from the smell of fresh paint to the 'new car' or 'new furniture' smell. Indoor VOC levels are often several times higher than outdoors because the sources are inside and ventilation is limited.
Common indoor sources
| Source | Typical VOCs | Pattern |
|---|---|---|
| Paints, varnishes, solvents | Toluene, xylene, white spirit | High when fresh, decays over days/weeks |
| Engineered wood (MDF, chipboard, plywood) | Formaldehyde | Ongoing off-gassing, worse when new/warm |
| New furniture, carpets, foams | Mixed VOCs, formaldehyde | Highest when new; 'new furniture' smell |
| Cleaning products, air fresheners | Limonene, terpenes, alcohols | Spikes during/after use |
| Adhesives, sealants, flooring | Various solvents | High during/after installation |
Formaldehyde — the one to watch
Formaldehyde is a specific VOC of concern: emitted by the resins in MDF, chipboard, plywood and some insulation and furnishings, it's an irritant and a recognised carcinogen at sufficient exposure. The WHO sets a short-term guideline of around 0.1 mg/m³ (0.08 ppm). Off-gassing is highest when materials are new and is accelerated by heat and humidity, easing over time.
Health effects
At typical indoor levels, VOCs are associated with the 'sick building' symptoms: eye, nose and throat irritation, headaches, and aggravation of asthma and allergies, with sensitive individuals affected more. Some specific VOCs (formaldehyde, benzene) carry more serious long-term risks. Because the mix is complex and individual sensitivities vary, the sensible strategy is precaution: reduce the sources and ventilate well.
What TVOC readings can and can't tell you
Controlling VOCs — source first, then ventilation
- Source control — choose low-VOC paints, finishes and adhesives, and low-formaldehyde (E1/E0 or formaldehyde-free) engineered wood and furnishings. This is by far the most effective step, because it removes the emission at source.
- Air out new materials — let new furniture, flooring and decoration off-gas with extra ventilation when first installed, when emissions are highest.
- Ventilate continuously — background and mechanical ventilation dilute the steady, low-level off-gassing of materials already in place; MVHR provides continuous fresh air to keep levels down.
- Manage activities — ventilate during and after painting, cleaning and any solvent use; reconsider routine air fresheners and scented candles, which add VOCs rather than removing them.