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  Formaldehyde, or HCHO, is a colorless gas at room temperature with an extremely pungent, suffocating aroma. It is a highly reactive gas, classified as a volatile organic compound (VOC).  The term volatile means that the compounds vaporize i.e., become a gas at room temperature.   
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Formaldehyde is an industrial chemical used widely in industry to manufacture building products, other chemicals, and household products.  In the home, formaldehyde is used as a coating or adhesive and comes in many synthetic resin mixtures. Some of the more common synthetic resins are phenol-formaldehyde (PF), malamine-formaldehyde (MF), and urea-formaldehyde (UF). UF is highly water-soluble and therefore is the most problematic mixture for indoor air pollution.

Common Sources

Formaldehyde synthetics are common indoors in composite wood products.  Mobile homes are especially at risk for indoor formaldehyde pollution because of their abundance of composite wood in construction and relatively compact interior space.  Formaldehyde gas can also be released into the air by burning wood, natural gas or kerosene, automobiles, and cigarettes.  It can off-gas from materials made with it and it may also occur naturally.

Pressed wood-products which may contain formaldehyde include particle board (used in sub-flooring and shelving), hardwood plywood paneling (used in decorative wall covering, cabinets and furniture), and medium density fiberboard (used in drawer fronts, cabinets and furniture tops). Medium density fiberboard is especially problematic because it contains between 2 and 4 times as much urea-formaldehyde as common particle board.

Another source of formaldehyde may be carpet backing and urea-formaldehyde foam insulation (UFFI).  In the 1970s, many homes were insulated with UFFI as an energy conservation measure before it was discovered that UFFI contained dangerously high levels of formaldehyde.  Fortunately, formaldehyde emissions in this product decline over time, so houses still using UFFI are unlikely to have high levels of formaldehyde now. This insulation is not very common in modern housing.

Other sources include preservatives in some paints, chemical coatings (such as those found in the permanent press quality applied to draperies and fabrics), and the finish texture used to coat some paper products.

All of these formaldehyde mixtures will release dangerous formaldehyde gas into the air unless they are properly sealed. During warmer months, problems with formaldehyde can be especially serious  as an increase in temperature of 5 to 6 degrees Celsius can double the gas's concentration.  Further, an increase in relative humidity from 30% to 70% can also cause the gas concentration to nearly double. If both temperature and humidity increase, the concentration of gas can rise to five times its original amount.

Health Effects

Early health symptoms of formaldehyde in the home include eye, nose, and throat irritation  as well as coughing and breathing difficulties.  If the problem reaches a serious level,  asthma attacks, nausea, vomiting, severe headaches, and nose bleeds can occur. The effects of short-term exposure are relatively small, as the health problems usually disappear once the pollutant has been removed. However, long-term exposure increases a person's sensitivity to the gas, increasing the  probability of health risk. Studies have shown that persons in high contact with the gas over a long period of time (such as biological scientists or morticians) experience a high risk of acquiring cancer. Those who have worked with or lived around the gas for 10 or more years are considered at high risk.

Formaldehyde has been known to cause cancer in laboratory animals and could possibly cause cancer in humans.  There is no known maximum threshold level and no known level below which there is not a threat of cancer.  The risk of getting cancer from formaldehyde depends upon the amount and duration of exposure.

Exposure Guidelines

Formaldehyde, because of its high danger level, is considered a potential human carcinogen and is therefore classified differently than most pollutants. It is normally present at low levels, usually less than 0.03 ppm (parts per million), in both indoor and outdoor air.

Levels above 0.1 ppm can cause acute health problems such as those mentioned above. The World Health Organization recommends that exposure should not exceed 0.05 ppm.


Levels of formaldehyde gas in the indoor air depend mainly upon [1] the source, [2] temperature, [3] humidity, and [4] the exchange rate of air entering or leaving the home.  As temperature rises, greater amounts of formaldehyde are emitted. When the temperature is lowered, less formaldehyde is emitted. Formaldehyde levels can change with the season and vary from day-to-day and day-to-night. Levels may also increase on a hot and humid day and decrease on a cool, dry day. Maintaining moderate temperatures and low (30 to 50 percent) relative humidity levels works best. Also, another control measure is to increasing the flow of outdoor air to the inside and vice versa so that the rate of air exchange is well balanced. Naturally, rural areas have lower concentrations while urban areas have higher concentrations.

In wood products, the easiest way to avoid problems with formaldehyde is to ask about the content of formaldehyde in pressed wood products including building materials, cabinets, and furniture before you purchase them. Try to avoid any products with urea-formaldehyde in them. There are plenty of building materials available which are formaldehyde free and exterior grade plywood can be used as a substitute for particle board. Although the exterior plywood may contain formaldehyde in some form, urea-formaldehyde is not used in exterior products and UF is the most problematic form of synthetic formaldehyde.  Exposure may be limited by purchasing products labeled as low-emitting or wood products made from phenol formaldehyde, exp. OSB - oriented strand board or softwood plywood.

If replacing the materials which contain formaldehyde is not possible, the gas can be sealed using either 2 coats of a water-based polyurethane sealant or a special formaldehyde sealant.  When sealing, make sure all of the unfinished material is coated, including the undersides of counter tops and ends of any boards. Another method of controlling the buildup of formaldehyde in the home can be through the use of a continuous, mechanical ventilation system to prevent concentration levels of the gas from increasing.

Tips on how to reduce exposure:

  • When purchasing pressed wood products (particleboard, MDF, or hardwood plywood), look for products that carry a ANSI label -American National Standards Institute (ANSI). The following standards indicate lower formaldehyde emission levels.  (Particleboard should conform to ANSI A208.1-1993.  For particleboard flooring, look for ANSI grades "PBU", "D2", or "D3".   MDF should comply with ANSI A208.2-1994; and hardwood plywood with ANSI/HPVA HP-1-1994).
  • Purchase furniture containing a higher percentage of paneled, laminated, or coated surfaces.  Non-laminated panels of pressed wood products generally emit more formaldehyde.
  • Increase ventilation in the home by opening doors and windows and installing exhaust fan(s).
  • Seal non-laminated surfaces of formaldehyde containing products with paints, varnish, or polyurethane-like materials.  Seal completely with materials that do not contain formaldehyde.  Note: some paints and coatings emit VOCs when curing so properly ventilate during and after treatment.

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