One survey reported formaldehyde levels ranging from 0.10 to 3.68 ppm in homes. The major sources appear to be power plants, manufacturing facilities, incinerators, and automobile exhaust emissions.
Smoking is another important source of formaldehyde.
Formaldehyde may also be present in food, either naturally or as a result of contamination. However, these measurements only appear to be useful when exposure to relatively large amounts of formaldehyde has occurred. Other effects seen from exposure to high levels of formaldehyde in humans are coughing, wheezing, chest pains, and bronchitis. Ingestion exposure to formaldehyde in humans has resulted in corrosion of the gastrointestinal tract and inflammation and ulceration of the mouth, esophagus, and stomach. 50 tests in rats and rabbits have shown formaldehyde to have high acute toxicity from inhalation, oral, and dermal exposure.