Funeral directors, who are typically exposed to formaldehyde while preparing bodies for burial, may be at heightened risk for the neurodegenerative disease amyotrophic lateral sclerosis (ALS), according to new research published in the Journal of Neurology, Neurosurgery & Psychiatry.

ALS awareness was significantly boosted last year as a result of the ice bucket challenge. Also known as Lou Gehrig’s disease, the disorder involves the death of neurons, and is progressive, meaning the symptoms worsen over time. Symptoms begin with muscle twitching, stiffness, and weakness, which leads to difficulty in speaking and breathing. This then continues on to paralysis, respiratory failure, and eventually death.

Many environmental factors have been investigated and debated as causes of ALS, formaldehyde among them.

Using the National Longitudinal Mortality Study (NLMS), which involves almost 1.5 million adults, researchers examined the link between ALS and occupational exposure to formaldehyde. Participants were asked about their current or most recent job, and their formaldehyde exposure level was estimated based on criteria developed by the National Cancer Institute. The intensity (frequency and level) and probability (likelihood) of exposure was determined for each job.

Results showed that men with a high probability of exposure to formaldehyde were about three times as likely to die of ALS as those who had not been exposed to the chemical at all. Men whose both intensity and probability were rated as high were over four times more likely to die of ALS than those with no exposure, though there were only two deaths in the group.

Women, however, did not show a difference in risk of ALS no matter what their probability of exposure. Researchers suggested that this could be because too few had jobs that exposed them to formaldehyde, making it difficult to calculate an accurate risk level.

All of the 493 men with both high intensity and probability of exposure to formaldehyde were funeral directors, as were almost all of the women, none of whom died of ALS.

The researchers hypothesized that the gender discrepancy could be due to differences in occupational responsibility within the job of funeral director. Women are more often involved in dealing with grieving relatives than actually embalming bodies, which would limit their exposure to formaldehyde.

This study is observational, meaning that no definitive conclusions can be drawn about cause and effect. Funeral directors are often exposed to various chemicals throughout their professional lives, along with bacteria and prions.

Formaldehyde: A Closer Look

Formaldehyde is a naturally occurring organic compound produced by plants, animals, and humans. It is also used in many household products and is commonly used as an industrial disinfectant. At room temperature, formaldehyde is a colorless, flammable gas with a pungent odor. It is quickly broken down in the air — generally within hours.

The main way humans are exposed to formaldehyde is through inhalation, usually after materials containing formaldehyde release it as a gas or vapor into the air. Funeral directors are exposed to the chemical through embalming fluids.

The most common short-term side effects of formaldehyde exposure include irritation of the eyes, nose, and throat; coughing, nausea, and skin irritation. Perhaps the most popular condition to be associated with formaldehyde exposure in the long-term is cancer. The National Toxicology Program (NTP), which is formed from departments of various government agencies including the National Institutes of Health (NIH), the Food and Drug Administration (FDA), and the Centers for Disease Control and Prevention (CDC), has listed formaldehyde as “known to be a human carcinogen.” Other agencies, including the Environmental Protection Agency (EPA) and the National Cancer Institute (NCI), have listed formaldehyde’s carcinogenic effects as “probable.”

Since the 1980s, the NIH and NCI have conducted studies attempting to link formaldehyde workplace exposure to cancer. Several of these studies produced results suggesting formaldehyde exposure could lead to a higher risk of cancer, with myeloid leukemia in particular exhibiting a strong link showing in those who had been exposed to the chemical.

The levels of formaldehyde in the brain increase with age, and with some neurodegenerative disorders. The chemical has been linked through experimental research to nerve damage, the production of harmful free radicals, and increased permeability of mitochondria — the energy powerhouses of the cell. All of these have been implicated in ALS, according to research.

Sources: Roberts A, Johnson N, Cudkowitz M, Eum K, Weisskopf M. Job-related formaldehyde exposure and ALS mortality in the U.S.A. Journal of Neurology, Neurosurgery & Psychiatry. 2015.

Hauptmann M, Stewart P, Lubin J, Beane Freeman L, Hornung R, Herrick R et al. Mortality from lymphohematopoietic malignancies and brain cancer among embalmers exposed to formaldehyde. Journal of the National Cancer Institute. 2009.

Tulpule K, Dringen R. Formaldehyde in brain: an overlooked player in neurodegeneration? Journal of Neurochemistry. 2013.