The World Health Organization’s indoor air guideline for formaldehyde is 0.1 mg/m³, measured as an average over any 30-minute period. That’s about 0.08 parts per million (ppm). WHO set the level to prevent sensory irritation of the eyes, nose and throat, and says it should not be exceeded in any 30-minute period during the day. According to WHO, keeping to that short-term guideline will also prevent long-term effects, including cancer. Readings below 0.1 mg/m³ are generally considered low for a home.
No single number makes a room “safe” for everyone, though, and a reading from a consumer monitor is not the same as a certified measurement. Here’s how to read the numbers.
mg/m³ and ppm
Formaldehyde levels are reported in two units. Milligrams per cubic meter (mg/m³) is a mass per volume. Parts per million (ppm) is a count of molecules. At normal room temperature, 1 ppm of formaldehyde is about 1.23 mg/m³, so:
| mg/m³ | ppm (approx.) |
|---|---|
| 0.05 | 0.04 |
| 0.1 | 0.08 |
| 0.123 | 0.1 |
| 0.37 | 0.3 |
| 1.0 | 0.81 |
Check which unit your device and your source use before you compare numbers. EPA, for example, often uses ppm. WHO uses mg/m³. FORMISENSE™ shows formaldehyde in mg/m³.
What the guideline is based on
WHO started from a controlled study in which eye irritation signs, such as more frequent blinking, appeared at about 0.6 mg/m³. It divided that by a safety factor of 5 to get 0.12 mg/m³, then rounded down to 0.1 mg/m³. WHO also assessed long-term effects, including cancer, and arrived at a value of about 0.2 mg/m³. Because that is higher than 0.1 mg/m³, WHO concluded that the short-term guideline protects against both.
EPA describes effects such as watery eyes, burning in the eyes and throat, nausea and difficulty breathing in some people exposed above 0.1 ppm, which is about 0.12 mg/m³. It also notes that high concentrations may trigger attacks in people with asthma, and that formaldehyde may cause cancer in humans.
What levels are typical in homes
WHO reports that average levels in homes are under 0.05 mg/m³, with concentrations above 0.2 mg/m³ showing up in new or renovated buildings, around new furnishings and in hot, humid weather. EPA reports that older homes without urea-formaldehyde foam insulation generally measure well below 0.1 ppm. Homes with a lot of new pressed-wood products can measure above 0.3 ppm, which is roughly 0.37 mg/m³ and more than three times the WHO guideline.
That’s why new furniture, new cabinets and newly built homes come up so often. EPA names pressed-wood products made with urea-formaldehyde glue, especially medium-density fiberboard, as likely the most significant formaldehyde sources in homes.
Reading your monitor
A handheld detector is good for comparison. If the nursery reads 0.15 mg/m³ and the living room reads 0.04, you know where to focus. If a reading drops after you ventilate, you know the ventilation is working.
Treat any single reading with some caution. EPA points out that low-cost indoor air monitors have limitations and only detect what their sensors are designed to measure. Readings can change with temperature, humidity and where the monitor is placed. Take several readings on different days before drawing conclusions.
As a rough guide for a home monitor that reads in mg/m³:
- Below 0.1 mg/m³ is within the WHO guideline. Keep ventilating as usual and recheck after anything new comes into the room.
- At or above 0.1 mg/m³ is above the guideline. Ventilate, look for likely sources, and test again.
- Readings that stay above the guideline after you’ve ventilated for several days are a reason to book a professional or laboratory test.
How to bring levels down
EPA’s advice is straightforward. Increase ventilation, particularly after bringing new sources into the home. Use air conditioning and dehumidifiers to keep temperature moderate and humidity low. Choose exterior-grade pressed-wood products, which use phenol-formaldehyde resin and emit less than those made with urea-formaldehyde resin.
For step-by-step testing, see how to test for formaldehyde at home.
Checking your own rooms
The FORMISENSE™ indoor air quality monitor reads formaldehyde from 0.000 to 1.99 mg/m³, which covers the WHO guideline and the higher levels EPA reports in homes with new pressed wood. It also shows TVOC, PM1.0, PM2.5, PM10, temperature and humidity. It’s a consumer monitor, not a medical device, and it doesn’t replace certified testing.