"VOC" is shorthand for any carbon-based compound volatile enough to be a gas at room temperature. The category is enormous: formaldehyde, benzene, toluene, terpenes, alcohols, ketones, the molecules that make perfume smell like perfume and a new car smell like a new car. Some are toxic at low concentrations (formaldehyde, benzene); most are merely irritants or allergens; many are harmless.
Indoor air is usually much more VOC-loaded than outdoor (typically 2× to 10× higher, sometimes 100× during a cleaning session or right after new furniture arrives). Sources include cooking (every cuisine has its own VOC signature), scented candles, cleaning sprays, paint, new carpet, vinyl flooring, particleboard, dry cleaning, and even people (we exhale acetone, isoprene, and a long tail of terpene metabolites).
There is no single ppm threshold that means "VOCs are bad," because the category is too broad. Instead, the SEN66 reports a Sensirion VOC index: a 0–500 score normalized against the last 24 hours of your own air. 100 is "the same as recently". 250+ means "something new just started emitting". This is more useful indoors than absolute ppb, because what counts as "high" depends on your baseline.
What to do: open a window when the VOC index spikes during cooking or cleaning, and let it settle before going back to baseline activities. For long-term reduction, ventilate continuously, choose low-VOC finishes when renovating, and air out new furniture before bringing it into a bedroom. For specific compound limits (formaldehyde, benzene) see California OEHHA reference exposure levels.
References
- EPA - Volatile organic compounds and indoor air www.epa.gov
- Sensirion - SEN66 datasheet and VOC index info sensirion.com
- California OEHHA - Reference exposure levels oehha.ca.gov
- NIOSH - Pocket Guide to Chemical Hazards www.cdc.gov
