Formaldehyde is a colorless, flammable, strong-smelling chemical that is used in 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. Formaldehyde also occurs naturally in the environment. It is produced in small amounts by most living organisms as part of normal metabolic processes.

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 source of formaldehyde exposure in the air is 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, certain 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.

When formaldehyde is present in the air at levels exceeding 0.1 ppm, some individuals may experience adverse effects such as watery eyes; burning sensations in 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.

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. Since that time, some studies of humans have suggested that formaldehyde exposure is associated with certain types of cancer. The International Agency for Research on Cancer (IARC) classifies formaldehyde as a human carcinogen. In 2011, the National Toxicology Program, an interagency program of the Department of Health and Human Services, named formaldehyde as a known human carcinogen in its 12 Report on Carcinogens.

Since the 1980s, the National Cancer Institute (NCI), a component of the National Institutes of Health (NIH), 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.

The long-term effects of formaldehyde exposure 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 surveys of professionals who are potentially exposed to formaldehyde in their work, such as anatomists and embalmers, have suggested that these individuals are at an increased risk of leukemia and brain cancer compared with the general population. However, specific work practices and exposures were not characterized in these studies. An NCI case-control study among funeral industry workers that characterized exposure to formaldehyde also found an association between increasing formaldehyde exposure and mortality from myeloid leukemia (4). For this study, carried out among funeral industry workers who had died between 1960 and 1986, researchers compared those who had died from hematopoietic and lymphatic cancers and brain tumors with those who died from other causes. (Hematopoietic or hematologic cancers such as leukemia develop in the blood or bone marrow. Lymphatic cancers develop in the tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases.) This analysis showed that those who had performed the most embalming and those with the highest estimated formaldehyde exposure had the greatest risk of myeloid leukemia. There was no association with other cancers of the hematopoietic and lymphatic systems or with brain cancer.

A number of cohort studies involving workers exposed to formaldehyde have recently been completed. 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 (5). 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 it was not associated with cumulative exposure. An additional 10 years of data on the same workers were used in a follow-up study published in 2009 (6). This analysis continued to show a possible link between formaldehyde exposure and cancers of the hematopoietic and lymphatic systems, particularly myeloid leukemia. As in the initial study, the risk was highest earlier in the follow-up period. Risks declined steadily over time, such that the cumulative excess risk of myeloid leukemia was no longer statistically significant at the end of the follow-up period. The researchers noted that similar patterns of risks over time had been seen for other agents known to cause leukemia.

A cohort 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 (7). However, the evidence remains mixed because a cohort study of 14,014 British industry workers found no association between formaldehyde exposure and leukemia deaths (8).

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 and case-control studies and the experimental data from laboratory research, NCI investigators have concluded that exposure to formaldehyde may cause leukemia, particularly myeloid leukemia, in humans.

In addition, several case-control studies, as well as analysis of the large NCI industrial cohort (6), have found an association between formaldehyde exposure and nasopharyngeal cancer, although some other studies have not. Data from extended follow-up of the NCI cohort found that the excess of nasopharyngeal cancer observed in the earlier report persisted (9).

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. The most recent data on lung cancer from the cohort study did not find any relationship between formaldehyde exposure and lung cancer mortality.

In 1987, OSHA established a Federal standard that reduced the amount of formaldehyde to which workers can be exposed over an 8-hour workday 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.

The EPA recommends the use of “exterior-grade” pressed-wood products to limit formaldehyde exposure in the home. These products emit less formaldehyde because they contain phenol resins, not urea resins. (Pressed-wood products include plywood, paneling, particleboard, and fiberboard and are not the same as pressure-treated wood products, which contain chemical preservatives and are intended for outdoor use.) 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.

If you decide that you want to make your hair less frizzy or straighter, you may choose to go to a professional stylist at a hair salon for a hair straightening or smoothing service. Most hair smoothing or straightening products release formaldehyde gas, a known human carcinogen as classified by the International Agency for Research on Cancer, into the air during the hair straightening or smoothing process. Formaldehyde exposure can cause both short- and long-term effects that may impact your health.

What Happens During the Hair Smoothing Process?

Your stylist usually applies a hair straightening or smoothing solution to your hair and follows it with a heat processing step—typically performed with a flat iron device that seals the solution into the strands of the hair. When the solution is heated, the formaldehyde in the product is released into the air as a gas. If the salon is not properly ventilated, you, your stylist, and others in the salon are at risk of inhaling the released formaldehyde.

Why Exposure to Formaldehyde is Dangerous

When formaldehyde is released into the air and is present in the air at levels exceeding 0.1 ppm, it can cause serious irritation of your eyes, nose, and lungs. It can also cause skin sensitivity or allergic dermatitis.

Formaldehyde Exposure: Potential Short-and Long-Term Effects

The greater the exposure to products that contain formaldehyde in terms of both length of time and concentration, the higher the potential health risks. Individuals who have experienced formaldehyde exposure have described reactions such as eye problems or irritation, nervous system problems (for example, headaches and dizziness), respiratory tract problems (sore or scratchy throat, cough, wheezing), nausea, chest pain, vomiting, and rashes. Chronic effects associated with formaldehyde can include an increased prevalence of headaches, asthma, contact dermatitis (a red, itchy rash caused by direct contact with a substance or an allergic reaction to it as a result of sensitization) and possibly cancer.

It’s important to note that some people are very sensitive to formaldehyde, whereas others have no reaction to the same level of exposure. If you are sensitive to formaldehyde, you should not use this type of product.

Steps to Take If You’re Thinking of Using Hair Smoothing Products

1. Don’t do it yourself. Don’t apply them yourself at home. Go to a licensed hair professional in a salon. Hair professionals should be trained to take precautions such as wearing gloves and safety glasses, as well as making sure that there is proper ventilation when applying hair smoothing products.
2. Read the list of ingredients. While the FDA discourages consumers from buying these products for home use, if you are considering purchasing a product from a store or online to apply yourself, read the required list of ingredients. If there isn’t one, don’t buy the product. If the hair smoothing product lists one of these ingredient names on the packaging or company website: formaldehyde, formalin, or methylene glycol, then it means the product contains formaldehyde or will release formaldehyde. Of note, not all hair smoothing products contain formaldehyde, which is why you need to read the label to see what is in the product.
3. You may also want to ask your salon professional these questions: Does the product contain formaldehyde? Is there an ingredient list available for this product that I could read? Would it be possible for me to review the Safety Data Sheet for this product? Have you been trained to apply this product, and do you know the necessary safeguards to minimize exposure to formaldehyde? May I see your training certificate from the manufacturer and the directions for product use? Does the salon have proper ventilation? Do you periodically test the air for adherence to the Occupational Safety and Health Administration’s limits for formaldehyde? Do you have an alternative hair smoothing product that does not release formaldehyde when heated?
4. Report bad reactions. If you experience a bad reaction to a hair smoothing product, stop using the product and report your symptoms to your health care provider. You can also report your symptom to the FDA by contacting the Consumer Complaint Coordinator in your area or by reporting them online at MedWatch, the FDA’s safety information and adverse reporting program. You also may call MedWatch at 1-800-332-1088 to request a reporting form by mail.