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Formaldehyde is normally present at low levels, usually less than 0.03 ppm, in both outdoor and indoor air. The outdoor air in rural areas has lower concentrations while urban areas have higher concentrations.

Residences or offices that contain products that release formaldehyde to the air can have formaldehyde levels of greater than 0.03 ppm. Products that may add formaldehyde to the air include particleboard used as flooring underlayment, shelving, furniture and cabinets; MDF in cabinets and furniture; hardwood plywood wall panels, and ureaformaldehyde foam used as insulation. As formaldehyde levels increase, illness or discomfort is more likely to occur and may be more serious.

Efforts have been made by both the government and industry to reduce exposure to formaldehyde. CPSC voted to ban urea-formaldehyde foam insulation in 1982. That ban was over-turned in the courts, but this action greatly reduced the residential use of the insulation product. CPSC, the Department of Housing and Urban Development (HUD) and other federal agencies have historically worked with the pressed wood industry to further reduce the release of the chemical from their products. A 1985 HUD regulation covering the use of pressed wood products in manufactured housing was designed to ensure that indoor levels are below 0.4 ppm. However, it would be unrealistic to expect to completely remove formaldehyde from the air. Some persons who are extremely sensitive to formaldehyde may need to reduce or stop using these products.

Formaldehyde levels in the indoor air depend mainly on what is releasing the formaldehyde (the source), the temperature, the humidity, and the air exchange rate (the amount of outdoor air entering or leaving the indoor area). Increasing the flow of outdoor air to the inside decreases the formaldehyde levels. Decreasing this flow of outdoor air by sealing the residence or office increases the formaldehyde level in the indoor air.

As the temperature rises, more formaldehyde is emitted from the product. The reverse is also true; less formaldehyde is emitted at lower temperature. Humidity also affects the release of formaldehyde from the product. As humidity rises more formaldehyde is released. The formaldehyde levels in a residence change with the season and from day-to-day and day-to-night. Levels may be high on a hot and humid day and low on a cool, dry day.

Understanding these factors is important when you consider measuring the levels of formaldehyde. Some sources-such as pressed wood products containing ureaformaldehyde glues, urea-formaldehyde foam insulation, durable-press fabrics, and draperies-release more formaldehyde when new. As they age, the formaldehyde release decreases.

• Use "exterior-grade" pressed wood products (lower-emitting because they contain phenol resins, not urea resins).
• Use air conditioning and dehumidifiers to maintain moderate temperature and reduce humidity levels.
• Increase ventilation, particularly after bringing new sources of formaldehyde into the home.

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