What helps them embalm human remains in mortuaries could also lead them into obtaining a crippling disease.

Scientists learned that those who inhale the fumes of formaldehyde could increase their risk of developing amyotrophic lateral sclerosis (ALS) up to three times the average.

Researchers at the Harvard T.H. Chan School of Public Health analyzed data gathered from almost 1.5 million participants from 1973. The participants each answered a survey about their jobs and were then followed until they died. The survey questions helped the team figure out if exposure to formaldehyde had anything to do with the participants' jobs.

Findings of the analysis were published online in the Journal of Neurology, Neurosurgery & Psychiatry, July 13.

"Of the approximately 500 men exposed to very high levels of formaldehyde, they were all funeral directors," said lead researcher Andrea Roberts.

Approximately 30,000 Americans are affected by ALS, also known as Lou Gehrig's disease. It damages the nerves and gradually paralyzes patients.

The survey led the team to conclude that men who have a high probability of being exposed to formaldehyde were three times more likely to have died due to ALS. Those with who have no probability of being exposed to formaldehyde, on the other hand, were not found to have been diagnosed with ALS.

The researchers were unable to obtain a calculation for women, as there were not enough numbers who had jobs that exposed them to formaldehyde.

The research team reported that of the men who died, only two were exposed to equally high levels of formaldehyde. These two men were funeral directors. Majority of all deaths totaling to 372 were in patients who had no probable formaldehyde exposure.

While a big chunk of the participants who died were not exposed to formaldehyde, the researchers stressed that the results should be cautiously interpreted. They noted that in the US, jobs with a high formaldehyde probability and intensity are uncommon, and that ALS is rare. While there were only two funeral directors among those who died of ALS, the team said it is worth looking at more closely.

Apart from its embalming purposes, formaldehyde is also used in making wood products, glue, a preservative in shampoo and in permanent press fabrics. It is popularly known as a preservative for biological samples, and at high exposures, is a probable human carcinogen.