Formaldehyde is a simple, highly reactive hydrocarbon that is used as a fixative in the pathology laboratory, as a fumigant, and in the manufacture of foam insulation, cosmetics, drugs, clothing, and furniture. It is also a major toxic component of photochemical smog. Formaldehyde is a strong allergen and irritant to which humans have a very low odor threshold (less than 1 ppm), and it is carcinogenic in the rat bioassay via the inhalation
Formaldehyde residues are major constituents of smog. An overwhelming percentage of the aldehyde in smog is formaldehyde. It is through smog that the general population is most broadly exposed. Because of its irritant and allergenic properties, formaldehyde is considered one of the possible etiologic agents involved in the well-documented asthma incidents that have occurred in relation to moderate to severe smog events. Another source of exposure to the general public in indoor air is off-gassing from fabrics and foam materials. These levels are considerably lower than photochemical smog concentrations, but they are more insidious because of the ambient nature of the exposure. In house fires, formaldehyde residues in fabrics and foams play a major role in the toxicity of smoke.
The greatest risk for injury from formaldehyde is in a workplace with minimal industrial hygiene measures. The greatest danger of formaldehyde is to those individuals who have compromised pulmonary function.