UFFI foam insulation in an old house (C) Daniel Friedman Formaldehyde Gas & Outgassing Hazards In Buildings
Where does formaldehyde come from, what levels are hazardous, how do we reduce the hazard?

  • FORMALDEHYDE HAZARDS - CONTENTS: Sources of formaldehyde gas or odors in buildings. Table of concentrations of formaldehyde outdoors & indoors compared with recommended exposure limits for residential buildings. Formaldehyde gas exposure limits. How to reduce formaldehyde exposure levels in a building. Current sources of formaldehyde gas concerns in buildings. Formaldehyde outgassing health concerns in FEMA trailers provided as temporary housing for Hurricane Katrina victims and in other mobile homes.
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Formaldehyde gas exposure health risks in homes, offices, other buildings:

This article describes the health risks of exposure to formaldehyde gas in air or water, and we describe the proper steps to detect, measure, and remove formaldehyde gas and formaldehyde gas emitting building products in order to improve indoor air quality in homes. We include a table of common levels of formaldehyde emissions found outdoors and inside buildings combined with common residential exposure limits for formaldehyde (HCHO).

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A Guide to Reducing Exposure to Formaldehyde Hazards in Indoor Air

Particle board with mold (C) Daniel Friedman

Article Contents

Above: mold contaminated particleboard countertop materials. This countertop was a source of both formaldehyde offgassing and two species of Aspergillus sp. mold.

[Click to enlarge any image or table]

Table of Formaldehyde Concentrations (Levels) Exposures & Recommended Exposure Limits

Formaldehyde, HCHO, or formalin is a colorless gas, a ubiquitous volatile organic compound (VOC) that occurs in nature, is a combustion product, and is widely used in building products, often in the form of resins used in glues or binders.

[Click to enlarge any image]

Table 7-7 given above left lists the Contributions of Formaldehyde to Room Air from various building materials and activities. Additional sources of formaldehyde in buildings have been reported since that table was drawn, including product outgassing discussed in detail at

It is normal for indoor levels of formaldehyde to be above outdoor levels, and high formaldehyde concentrations may be found in some buildings, typically as a result of offgassing of formaldehyde from a variety of building products and furnishings.

Salthammer (2010) reported on the range of formaldehyde concentrations in both outdoor air and in building indoor air, from which we excerpt and into which we expand with formaldehyde level notes from other sources:

Common Concentrations of Formaldehyde (HCHO) in Indoor & Outdoor Air1

Type of Air / Location Approximate Formaldehyde Level in Parts per Billion (PPB) Comments
Remote Air 0.1 - 1 ppb  
Rural Air 0.5 - 1.5 ppb  
Urban Air 1.25 - 50 ppb  
Outdoor Air2 < 1 ppb - 6.5 ppb
[Median = 1.7 ppb]
Normal Indoor Air 15 - 100 ppb  

California EPA (OEHHA) Recommended Indoor Chronic Exposure Limit (residential) (REL)3 &
Recommended 8-hour exposure level limit

7.3 ppb To protect against respiroatory system effects3
California OEHHA3 30 ppb Decreased lung function in children
Canadian Residential IAQ Recommended Indoor 8-Hour Exposure Limit 40 ppb Respiratory symptoms may occur in children
California EPA (OEHHA) Recommended Indoor Acute 1-hour Exposure Limit (residential)
Acute Reference Exposure Level (REL)3
45 ppb Set to protect against sensory & eye irritation
California OEHHA3 60-120 ppb Children more likely to have asthma or chronic bronchitis
Canadian Residential IAQ Recommended Indoor 1- Hour Exposure Limit 100 ppb Eye irritation may occur
US EPA 100 ppb Respiratory irritation in most adults
California Study of Recently-Built Homes2 4 - 120 ppb
[Median = 29 ppb]
Polluted Indoor Air 100 - 400 ppb  
Extreme Conditions > 400 ppb  

1. Salthammer (2010)
2. Offermann (2009)
3. California OEHHA - Office of Environmental Health Hazard Assessment, cited by Offermann (2010).
See REFERENCES for citation details.

In sum it would be unusual to find indoor building air with a formaldehyde concentration below 1 ppb, and when the indoor formaldehyde concentration is above 100 ppb further investigation may be warranted.

See FORMALDEHYDE GAS EXPOSURE LIMITS for a table of Health Effects of Exposure to Formaldehyde and for formaldehyde exposure standards around the world.

Formaldehyde appears in many building components or contents such as fabrics, finishes, furniture, furnishings, plywood, OSB, MDF, particle board and other wood products. Formaldehyde-resin-containing wood panel type products are in turn used in the construction of cabinets, laminate flooring, shelving, wall & roof sheathing, subflooring or underlayment: all products having widespread use in buildings.

At above-left is an example of mold-contaminated particleboard used as the structure for a kitchen countertop.

Formaldehyde or resin containing it appears as well even in paper, pulp, and some insulations such as flass wool and rock wool. HCHO is so widely used because of its desirable properties and its low cost. It is thus a valuable compound that is not easily replaced in thse applications.

Because formaldehyde is a simple but highly-reactive organic chemical compound, nearly all products made using formaldehyde outgas or "offgass" formaldehyde to some extent. Some of these can contribute to indoor air quality problems. Formaldehyde outgassing from products typically is highest when the products are new and decreases significantly over time. The rate of decrease in formaldehyde outgassing also depends on the product composition and on conditions where it is found.

The level and duration of formaldehyde release from a product depends on quite a few variables discussed in this article series including temperature, physical movement or cutting, moisture or humidity level, how the product was made or how it has been coated or sealed.

Formaldehyde is used to add permanent press qualities to clothing and drapes, as a preservative in many paints and coatings, and as the adhesive resin in some carpeting, fiberglass insulations, and pressed wood products. It is also a product of combustion found in tobacco smoke and the fumes from gas stoves and other unvented combustion.

By far, the most significant source of formaldehyde in homes today is pressed wood products (also referred to as composite wood products or particle board or medium density fiberboard or MDF) made with urea- formaldehyde resins. These products include particle board, interior hardwood paneling, some laminate flooring products and medium-density fiberboard (MDF), which has the highest concentration of urea- formaldehyde of any pressed wood product. The relative contributions of new materials to a single room are shown in Table 7-7, above-left.

Formaldehyde is normally present at low levels, usually below 0.03 ppm both indoors and outdoors. However, buildings with high levels of pressed wood products can have higher indoor levels. For example, many manufactured homes have levels well above 0.03 ppm, due to their relatively small volume and large surface area of formaldehyde emitting materials.

HUD standards that limit the formaldehyde emissions of materials used in manufactured housing are designed to bring the ambient level to below 0.40 ppm, still over four times the 0.10 ppm limit recommended by most health and standards organizations, including ASHRAE and ANSI.

No standard exists for site- built homes.

Health Effects of Formaldehyde

Table of Formaldehyde exposure limits (C) J Wiley, Steven BlissSensitivity to formaldehyde varies widely. At low levels in buildings formaldehyde has virtually no smell or "odor".

At levels between 0.40 and 3.0 ppm, most people experience watery eyes, burning sensations in the nose or throat, nausea, and difficulty breathing. Most people detect the chemical’s pungent odor at about 0.80 ppm, but many can smell it at concentrations as low as .05 ppm.

Watch out: there may be health risks from exposure to formaldehyde even if there is no formaldehyde-related odor detected or reported by building occupants.

Formaldehyde been identified as a human cancer-causing agent (IARC, 2004).

Formaldehyde & Asthma

High concentrations of formaldehyde may trigger asthma attacks, and there is strong evidence that some people can develop a sensitivity to formaldehyde from exposure.

[Click any image or table to see an enlarged, detailed version]

Formaldehyde as a Carcinogen

Formaldehyde has been conclusively linked to nasal cancer in rats, while human studies have suggested a link to nose and throat cancer in humans, but are not conclusive.

Based on the current evidence the EPA and the International Agency for Research in Cancer consider formaldehyde a probable carcinogen prompting the lower workplace limits suggested by the National Institute for Occupational Safety and Health (NIOSH) (see the Formaldehyde Exposure Limits in Table 7-8 at left).

More information is at Formaldehyde Exposure in Homes:A Reference for State Officials to Use in Decision-making [PDF]

-- Above material was adapted with permission from Best Practices Guide to Residential Construction. Updated through January 2014.

Common Sources of Formaldehyde Gas in buildings

Table of formaldehyde sources indoors (C) J Wiley, Steven Bliss

at FORMALDEHYDE HAZARDS we report that formaldehyde is a ubiquitous volatile organic compound (VOC) that occurs in nature and is widely used in building products, finishes, and furnishings because of its desirable properties and low cost. Nearly all products made with formaldehyde outgas to some extent, but only a few contribute significantly to indoor air problems.

A significant source of indoor formaldehyde emissions in many buildings is found in flooring, furnishings, shelving or other products making use of medium density fiberboard (MDF) but note that the levels of outgassing among even these products may vary widely depending on the manufacturing method and source, product age, building and building environment factors such as temperature, humidity, ventilation, air circulation and other considerations.

[Click to enlarge any image]

Formaldehyde is used to add permanent press qualities to clothing and drapes, as a preservative in many paints and coatings, and as the adhesive resin in some carpeting, fiberglass insulations, and pressed wood products. It is also a product of combustion found in tobacco smoke and the fumes from gas stoves and other unvented combustion.

Table 7-7 at left lists the Contributions of Formaldehyde to Room Air from various building materials and activities.

Additional sources of formaldehyde in buildings have been reported since that table was drawn, including product outgassing are discussed in detail

Research on Formaldehyde Sources (including particleboad) in Buildings

Relationship Between Building Air Change Rate and Formaldehyde Levels

Offermann and Kincaid writing for The Synergist (AIHA) reported in 2010 that while most building codes require at least one air change per hour (ACH) in office buildings, residential ACH rates have had less attention. The authors explain that as homes have been made increasingly air-tight (to save energy) the home ventilation rate can be much less than the commercial or industrial standard and may be as low as 0.1 ACH. (Offermann 2010)

The authors note that a 2005 IAQ study found that 67% of California homes had a fresh air intake or ACH rate below the 2006 Califorina required rate of 0.35 ACH. The same study found that indoor levels of formaldehyde also exceeded the California recommendations. Still more remarkably for people who have not been following research concerning the safety of exposure to formaldehyde, all of the California homes studied were found to sport formaldehyde at levels defined as the California No Significant Risk Level (NSRL) for cancer.

California Building Standards (Title 24) now require a minimal 0.15 ACH provision of outdoor air for homes built after 1 January 2010.

The authors propose that the most likely source of this formaldehyde indoors is composite wood products made with formaldehyde resins (see FORMALDEHYDE GAS SOURCES in BUILDINGS) combined with the low fresh air exchange rate associated with these low ACH numbers.

Yellow resin binding fiberglass insulation (C) Daniel FriedmanIn the 2010 Synergist article Kincaid reportind finding higher than usual levels of formaldehyde in homes in Los Altos CA (60-120 ppb) with still higher levels of several hundred ppb of formaldehyde in "normally closed" spaces such as closets and pantries.

Kincaid noted that "In nearby San Jose and surrounding communities, formaldehyde concentrations in homes was typically between 40 and 80 ppb." 3 The authors pose that the higher levels of formaldehyde in Los Altos homes was associated with efforts to promote green construction and tighter buildings - all of the homes she had tested were "GreenPoint" rated.

Further studies reported by the authors, finding higher concentrations (50-80 ppb) of formaldehyde in Indio CA homes built in 2007, suggested that elevated levels of formaldehyde in wall cavities were due to two formaldehyde emitters: drywall and fiberglass insulation [presumably the binder resins typically used with formaldehyde - Ed.].

Indeed binder resin such as the yellow resin in our lab photo at above left, is what usually gives fiberglass insulating products their characteristic color - glass fibers themselves are generally hyaline or colorless.

The authors concluded [and we agree] that the essential cause of high indoor formaldehyde levels in buildings is the combination of formaldehyde offgassing sources such as particleboard or some brands of flooring and other products combined with low ACH or fresh air or make-up air in buildings.
see VENTILATION, BALANCED for advice on using heat-recovery ventilation to improve indoor air quality while preserving low energy cost designs in buildings.

Formaldehyde Article Series Contents


Continue reading at FORMALDEHYDE GAS SOURCES in BUILDINGS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see FORMALDEHYDE GAS HAZARD REDUCTION - how to remove, avoid, or eliminate indoor formaldehyde gas hazards


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