Formaldehyde and Cancer Risk

• Key Points
  Formaldehyde is a colorless, flammable, strong-smelling chemical that is used to manufacture building materials and to produce many household products (see Question 1).
• Formaldehyde sources in the home include pressed-wood products, cigarette smoke, and fuel-burning appliances (see Question 2).
• When exposed to formaldehyde, some individuals may experience various short-term health effects (see Question 3).
• Formaldehyde has been classified as a known human carcinogen (cancer-causing substance) by the International Agency for Research on Cancer and as a probable human carcinogen by the U.S. Environmental Protection Agency (see Question 4).
• Research studies of workers exposed to formaldehyde have suggested an association between formaldehyde exposure and cancers of the nasal sinuses, nasopharynx, and brain, and possibly leukemia (see Questions 4, and 5).

1. What is formaldehyde?
Formaldehyde is a colorless, flammable, strong-smelling chemical that is used to manufacture building materials and to produce many household products. It is used in pressed-wood products, such as particleboard, plywood, and fiberboard; glues and adhesives; permanent-press fabrics; paper product coatings; and certain insulation materials. In addition, formaldehyde is commonly used as an industrial fungicide, germicide, and disinfectant, and as a preservative in mortuaries and medical laboratories.

2. How is the general population exposed to formaldehyde?
According to a 1997 report by the U.S. Consumer Product Safety Commission, formaldehyde is normally present in both indoor and outdoor air at low levels, usually less than 0.03 parts of formaldehyde per million parts of air (ppm). Materials containing formaldehyde can release formaldehyde gas or vapor into the air. One example of formaldehyde exposure in the air is through automobile tailpipe emissions.

During the 1970s, urea-formaldehyde foam insulation (UFFI) was used in many homes. However, few homes are now insulated with UFFI. Homes in which UFFI was installed many years ago are not likely to have high formaldehyde levels now. Pressed-wood products containing formaldehyde resins are often a significant source of formaldehyde in homes. Other potential indoor sources of formaldehyde include cigarette smoke and the use of unvented fuel-burning appliances, such as gas stoves, wood-burning stoves, and kerosene heaters.

Industrial workers who produce formaldehyde or formaldehyde-containing products, laboratory technicians, health care professionals, and mortuary employees may be exposed to higher levels of formaldehyde than the general public. Exposure occurs primarily by inhaling formaldehyde gas or vapor from the air or by absorbing liquids containing formaldehyde through the skin.

3. What are the short-term health effects of formaldehyde exposure?
When formaldehyde is present in the air at levels exceeding 0.1 ppm, some individuals may experience health effects, such as watery eyes; burning sensations of the eyes, nose, and throat; coughing; wheezing; nausea; and skin irritation. Some people are very sensitive to formaldehyde, whereas others have no reaction to the same level of exposure.

4. Can formaldehyde cause cancer?
Although the short-term health effects of formaldehyde exposure are well known, less is known about its potential long-term health effects. In 1980, laboratory studies showed that exposure to formaldehyde could cause nasal cancer in rats. This finding raised the question of whether formaldehyde exposure could also cause cancer in humans. In 1987, the U.S. Environmental Protection Agency (EPA) classified formaldehyde as a probable human carcinogen under conditions of unusually high or prolonged exposure (1). Since that time, some studies of industrial workers have suggested that formaldehyde exposure is associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukemia. In 1995, the International Agency for Research on Cancer (IARC) concluded that formaldehyde is a probable human carcinogen. In June 2004, after evaluating all existing data, the IARC reclassified formaldehyde as a known human carcinogen (2).

5. What have scientists learned about the relationship between formaldehyde and cancer?
Since the 1980s, the National Cancer Institute (NCI), a component of the National Institutes of Health, has conducted studies to determine whether there is an association between occupational exposure to formaldehyde and an increase in the risk of cancer. The results of this research have provided EPA and the Occupational Safety and Health Administration (OSHA) with information to evaluate the potential health effects of workplace exposure to formaldehyde.

Long-term effects of formaldehyde have been evaluated in epidemiologic studies (studies that attempt to uncover the patterns and causes of disease in groups of people). One type of epidemiologic study is called a cohort study. A cohort is a group of people who may vary in their exposure to a particular factor, such as formaldehyde, and are followed over time to see whether they develop a disease. Another kind of epidemiologic study is called a case-control study. Case-control studies begin with people who are diagnosed as having a disease (cases) and compare them to people without the disease (controls), trying to identify differences in factors, such as exposure to formaldehyde, that might explain why the cases developed the disease but the controls did not.

Several NCI studies have found that anatomists and embalmers, people who are potentially exposed to formaldehyde in their professions, are at an increased risk of leukemia and brain cancer compared with the general population. In 2003, a number of cohort studies were completed among workers exposed to formaldehyde. One study, conducted by NCI, looked at 25,619 workers in industries with the potential for occupational formaldehyde exposure and estimated each worker’s exposure to the chemical while at work (3). The results showed an increased risk of death due to leukemia, particularly myeloid leukemia, among workers exposed to formaldehyde. This risk was associated with increasing peak and average levels of exposure, as well as with the duration of exposure, but not with cumulative exposure. Using an additional 10 years of data, a follow-up study published in 2009 continued to show a possible link between formaldehyde exposure and cancers of the hematopoietic and lymphatic systems, particularly myeloid leukemia, as was previously reported (4). As in the previous study, the risk was highest earlier in the follow-up period and declined steadily over time, such that the cumulative excess risk of myeloid leukemia was no longer statistically significant. The researchers noted that similar patterns of risks over time had been seen for other agents known to cause leukemia.

A separate study of 11,039 textile workers performed by the National Institute for Occupational Safety and Health (NIOSH) also found an association between the duration of exposure to formaldehyde and leukemia deaths (5). However, the evidence remains mixed because a cohort study of 14,014 British industry workers found no association between cumulative formaldehyde exposure and leukemia deaths (6).

Formaldehyde undergoes rapid chemical changes immediately after absorption. Therefore, some scientists think that formaldehyde is unlikely to have effects at sites other than the upper respiratory tract. However, some laboratory studies suggest that formaldehyde may affect the lymphatic and hematopoietic systems. Based on both the epidemiologic data from cohort studies and the experimental data from laboratory research, NCI investigators have concluded that exposure to formaldehyde may cause leukemia, particularly myeloid leukemia, in humans. However, inconsistent results from other studies suggest that further research is needed before definite conclusions can be drawn.

Several case-control studies and cohort studies, including analysis of the large NCI cohort, have reported an association between formaldehyde exposure and nasopharyngeal cancer, although some other studies have not. Data from extended follow-up of the NCI study found that the excess of nasopharyngeal cancer observed in the earlier report persisted (7).

Earlier analysis of the NCI cohort found increased lung cancer deaths among industrial workers compared with the general U.S. population. However, the rate of lung cancer deaths did not increase with higher levels of formaldehyde exposure. This observation led the researchers to conclude that factors other than formaldehyde exposure might have caused the increased deaths. New data on lung cancer from the extended follow-up did not find any relationship between formaldehyde exposure and lung cancer mortality.

6. What has been done to protect workers from formaldehyde?
In 1987, OSHA established a Federal standard that reduced the amount of formaldehyde to which workers can be exposed over an 8-hour work day from 3 ppm to 1 ppm. In May 1992, the standard was amended, and the formaldehyde exposure limit was further reduced to 0.75 ppm.

7. How can people limit formaldehyde exposure in their homes?
The EPA recommends the use of “exterior-grade” pressed-wood products to limit formaldehyde exposure in the home. Before purchasing pressed-wood products, including building materials, cabinetry, and furniture, buyers should ask about the formaldehyde content of these products. Formaldehyde levels in homes can also be reduced by ensuring adequate ventilation, moderate temperatures, and reduced humidity levels through the use of air conditioners and dehumidifiers.

8. More information

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