Typical formaldehyde levels in homes
People often ask what a “normal” or “acceptable” formaldehyde level is, so here is the context. There is no single legally binding limit for formaldehyde in US homes; instead, health bodies publish guidelines. The most widely used is the World Health Organization’s 0.1 mg/m³ (about 0.08 ppm) over any 30-minute period.
n| Setting | Typical formaldehyde level |
|---|---|
| Outdoor air (urban) | about 0.011 to 0.020 ppm |
| Older homes without added pressed wood | generally well below 0.1 ppm |
| WHO indoor guideline | 0.1 mg/m³ (about 0.08 ppm) over 30 minutes |
| Homes with a lot of new pressed-wood products | can exceed 0.3 ppm |
| New or manufactured homes | often higher than older conventional homes |
For a sense of what is normal: the US EPA reports that average concentrations in older homes without urea-formaldehyde foam insulation are generally well below 0.1 ppm, while homes with significant amounts of new pressed-wood products can exceed 0.3 ppm. New and manufactured homes tend to read higher than older conventional homes, mainly because of newer composite-wood furniture, cabinetry and finishes.
mg/m³ and ppm: how the units compare
Guidelines and monitors don’t all use the same unit, so here is the conversion at normal room temperature (1 ppm formaldehyde is about 1.23 mg/m³):
n| mg/m³ | ppm (approx.) | ppb (approx.) |
|---|---|---|
| 0.03 | 0.024 | 24 |
| 0.05 | 0.04 | 40 |
| 0.1 (WHO guideline) | 0.08 | 80 |
| 0.37 | 0.3 | 300 |
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.
Sources
- World Health Organization, WHO Guidelines for Indoor Air Quality: Selected Pollutants, chapter on formaldehyde
- US EPA, What should I know about formaldehyde and indoor air quality?
- US EPA, Low-cost air pollution monitors and indoor air quality
If your high readings came from a recent purchase, see how long new furniture off-gasses formaldehyde.
nnnFrequently asked questions
What is an acceptable formaldehyde level in a home?
There is no single legally binding US limit, but the widely used WHO guideline is 0.1 mg/m³ (about 0.08 ppm) over any 30-minute period. Readings below that are generally considered acceptable for a home.
What is a normal formaldehyde level in homes?
EPA reports older homes without urea-formaldehyde insulation are generally well below 0.1 ppm, while homes with a lot of new pressed wood can exceed 0.3 ppm. Newer and manufactured homes usually read higher than older ones.
What are the formaldehyde ppm limits?
The WHO indoor guideline is about 0.08 ppm over 30 minutes. For workplaces, the US OSHA permissible limit is far higher at 0.75 ppm over 8 hours, but that is an occupational standard for healthy adults, not a target for homes.
What is a safe HCHO level?
HCHO is the chemical formula for formaldehyde, so a safe HCHO level is the same as a safe formaldehyde level: below the WHO guideline of 0.1 mg/m³ (0.08 ppm). Monitors that display HCHO usually show it in mg/m³.
nYour monitor also shows particle readings. See PM1.0, PM2.5 and PM10 explained.
nnSetting up a nursery? See formaldehyde in the nursery.
n