Leading Dry Cleaning Chemical Perchloroethylene Known to Cause Cancer

NIOSH Study of Dry-Cleaning Workers Shows Hazards of Perchloroethylene

Most dry cleaners use perchloroethylene

In 1996, the National Institute for Occupational Health (NIOSH) took a look at the cancer risks faced by workers at dry cleaners. They found that the leading dry cleaning chemical, perchloroethylene, is indicated in causing several types of cancer.

Below is the reprinted archive of the study results from the NIOSH website.

NOTICE: These are NIOSH Archive Documents, and may not represent current NIOSH Policy. They are presented here as historical content, for research and review purposes only. This collection of Worker Notification Materials and any recommendations made herein are relevant for specific worker populations. The results do not predict risk for a given individual. The results may not be universally applicable.

Study Background

The National Institute for Occupational Safety and Health (NIOSH) conducts research on workers’ health. Our scientists completed a study of 1708 men and women who had worked for at least one year before 1960 in a dry cleaning shop that used perchloroethylene. We got the names and work records from the dry-cleaning workers’ unions in the metropolitan areas around New York City; Detroit, Michigan; Chicago, Illinois; and Oakland/San Francisco, California. We studied the workers through 1996. The following has information about what the study found.

Why We Did the Study

Workers at dry-cleaners often breathe fumes from dry-cleaning fluids (also known as solvents). Workers also are exposed to solvents through their skin.

Most dry-cleaning machines now use perc (perchloroethylene, PCE). Some machines also use other solvents, usually Stoddard solvent.

The NIOSH study was done to confirm earlier reports that showed an increased risk of bladder cancer among workers in dry-cleaning. We also know that animals exposed to relatively high levels of perchloroethylene fumes develop other types of cancer.

Therefore, we studied all types of cancers. We also looked at other diseases and health problems that might be related to working in dry-cleaning shops.

It is important to remember that the results of the NIOSH study refer to dry cleaning workers as a group.

These results cannot be used to predict the future health of any individual worker.

How We Did the Study

The study included 1708 men and women who had worked for at least one year before 1960 in a dry cleaning shop that used perchloroethylene. We got the names and work records from the dry-cleaning workers’ unions in the metropolitan areas around New York City; Detroit, Michigan; Chicago, Illinois; and Oakland/San Francisco, California. We studied the workers through 1996.

We divided all of the workers into two groups. The perc-only group included 625 individuals who worked in dry-cleaning shops which used only perchloroethylene as a cleaning solvent. The mixed-solvent group included 1083 workers. These individuals each worked for at least one shop that used perc and at least one shop that used another dry cleaning solvent, usually Stoddard solvent.

We reviewed the death certificates of workers who had died. We counted the number of workers who died from each disease. Then we calculated the number of deaths from each disease that we would expect to find in the workers, based on how often people die of these diseases in the entire U.S. population.

The expected number of deaths takes into account the age, sex, and race of all the workers. If the number of deaths among these workers is higher than the expected number, then working with dry-cleaning solvents might be the cause.

Diseases such as cancer take many years to develop. Therefore, we looked at cancer risk at least twenty years after the workers started working in the dry cleaning industry. We wanted to see if those who worked with dry-cleaning solvents a longer time ago had a higher risk of developing cancer. Also, if solvent exposure is related to cancer, those with a longer exposure (five years or longer) should have a higher risk than those who were exposed for a lesser


What the Study Found

When we looked at underlying causes of death in the overall group, we found an increased risk of several different cancers and other diseases in the study group. The group that worked in dry cleaning shops where only perc was used included only 625 workers, a relatively small study group. Because of its small size, we could not draw strong conclusions about the health effects we observed in that group alone.

The chart below tells you about the diseases we found in the overall study group. The following information will help you understand the columns in chart:

Column 1: The number of deaths we observed for each disease in the study group.

Column 2: The number of deaths we would expect in the study group based on U.S. death rates

Column 3: The O/E ratio represents the number of deaths observed in the study group divided by the number of deaths we expected. The resulting number tells you how much more (or less) the mortality from each disease outcome is, compared to others in the U.S. who are not exposed to perchloroethylene and other dry cleaning solvents.

If the O/E ratio in the study group is a number greater than “1”, that means there was an increase in deaths from that disease in the study group.

For example, in the disease category of “all cancers combined”, we found 271 but expected about 217. This is an excess of 54 deaths. To get the O/E ratio, we divided 271 by 217. In this case, the ratio in deaths is 1.25. This means that the increase in deaths from all cancers combined was one and a quarter times more deaths than we expected.

Column 4: This column contains other comments about the particular disease outcome.

Table of Notifiable Diseases Among Workers in the NIOSH Study of Perc and Other Solvent Exposure

Cause of Death

Number Observed

Number Expected


Notes and Comments

All Cancers Combined




Bladder Cancer




Smoking is a risk factor

Cervical Cancer




Socio-economic factors are known to contribute

Esophageal Cancer




Smoking and alcohol use are risk factors





Tongue Cancer




Smoking and use of other tobacco products are risk factors

Lung Cancer








All over 65 years old

Stomach and Duodenum Disease




Was not related to length of employment

Urinary Stones




Found in perc-only group

What the Study Found in the “Perc Only” Group

Since the “perc only” sub-group is relatively small (625 workers), we cannot draw strong conclusions about the findings in that group. However, deaths from cancer of the tongue were statistically significantly increased in this group. Workers in this group, who had worked around perc for five or more years and who had 20 or more years since they first were exposed to perc also had a statistically significant increased risk for cancer of the esophagus.

For non-cancer outcomes, deaths from urinary stones were observed only in this sub-group. There were 2 deaths observed, both among white males.

Deaths from ischemic heart disease (IHD) also were statistically significantly increased in this subgroup. We found 93 IHD deaths but expected only about 73.

Details of the Overall Cancer Findings

In the overall group, those who worked for five years or more with perchloroethylene had a higher risk of bladder, esophageal, and cervical cancer, although most of these workers also had exposure to other solvents.

Increases in intestinal (mostly colon), lung, and pancreatic cancers also were observed mainly among the workers who were exposed to perc and other solvents. Therefore it is not possible to determine what may have caused the increase. The cause may have been perc alone, another solvent, or something else altogether.

Where other studies have suggested a possible relationship between perc and cancers of the liver and kidney, the NIOSH study did not find statistically significant increases in these two cancers.

Details of the Overall Non-Cancer Findings

Most of the increases in causes of death from non-cancer diseases seen in the NIOSH study were diseases of the respiratory and digestive systems, and of the heart. For example, we saw an increase in deaths from pneumonia, all of which were among workers over age 65. We observed 43 pneumonia deaths in the overall group, but expected only 28.

We also found 2 1/3 times more deaths from diseases of the stomach and duodenum than expected. This increase was not related to the length of employment. Most of these were ulcer deaths.

The number of deaths from ischemic heart disease (IHD) in the overall group was about what we expected. However, for those who worked in the perc-only shops, we observed 93 deaths from IHD, about 1� times more deaths than expected.

Last, for diseases of the urinary system, we saw an increase of urinary stones. We observed 2 deaths, both in white males who had been exposed to perc for more than 5 years. Both deaths were found in workers from dry cleaning shops which used perc only.

Study Findings in the Four Geographic Sub-Groups

The workers in this study worked in and around four major U.S. cities: Oakland/San Francisco, CA; Chicago IL; Detroit, MI,; and New York, NY. Mortality among workers in the four sub-groups representing these locations was analyzed using local (county) mortality rates as well as U.S. rates (1960-1996).

In general, the results for the four geographical sub-groups were consistent with the results for the overall group of workers. These results generally suggest that geographical variation in mortality does not account for the observed increases in any disease outcome. In addition, the increases we observed in the NIOSH study have remained elevated throughout the 1990s.

Effects of Smoking

Smoking increases the risk of all of the cancers we found in this study. We did not have information on the smoking habits on the workers in our study. However the risk of lung cancer was not highly increased among the workers in this study. This suggests that the workers may not have smoked excessively.

Smoking also increases the risk of heart and respiratory disease. If you smoke, you should stop.

The use of other tobacco products such as chewing tobacco and snuff also is bad for your health. They can cause cancer of the inside the mouth, as well as other illnesses.

For information on how to stop smoking, call the American Cancer Society (ASC) at 1-800-227-2345.

ACS has programs and information on ways to stop smoking. They also have free information on the treatment and diagnosis of various cancers. You may visit the ACS web site at www.cancer.org.

The American Lung Association also has programs to help you stop smoking. For information, call 1-800-LUNG-USA. (That’s 1-800-586-4872.)

Effects of Alcohol

Alcohol consumption also can contribute to the risk of some of the health effects observed in the NIOSH study. As with smoking habits, we did not have information on alcohol use among the workers in the study. If you drink alcohol, you should do so in moderation.

Limitations of the Study

“Limitations” are the facts which make the study findings less certain. There were four basic limitations in this study:

We did not have job titles for 2/3 of the workers. We also did not have personal exposure measurements for any worker. If we had this information, we could have drawn more accurate conclusions about the effects of exposure to the solvents.

We do not know how much factors like smoking, drinking alcohol, diet, and other lifestyle factors may have affected the study results.

We did not know exactly which solvents besides perchloroethylene and Stoddard solvent, workers were exposed to.

We did not have updated work history information on everyone in the cohort. Therefore the period of time that workers were exposed to dry-cleaning solvents may be underestimated.

What Other Studies Have Found

Studies by the National Cancer Institute and by other researchers also have found excess bladder, esophageal, and cervical cancer deaths among groups of dry-cleaning workers. Some of the studies used union records which included laundry workers, because they belonged to the same unions as the dry cleaners. Therefore the findings in these studies also included workers who had jobs in other occupations, as well as dry-cleaning.

Perchloroethylene and Other Solvent Levels

About 90% of all dry-cleaning plants still use perchloroethylene as a dry-cleaning fluid. If you still work in dry-cleaning, you probably are exposed to perc. NIOSH believes that perc is a potential cancer-causing agent. Therefore, exposures to perc should be reduced to the lowest possible level.

NIOSH exposure studies have shown that levels of less than 5 parts per million (ppm) over an 8-hour day are possible with well-maintained 4th generation machines.

OSHA Rules on Dry Cleaning Solvent Exposure Limits

The Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for perchloroethylene is 100 ppm over an 8-hour time-weighted average. A peak exposure should not exceed 200 ppm. for 5 minutes in any 3-hour period. In California and a few other states, the PEL is 25 ppm.

Some plants still use Stoddard solvent. This solvent irritates the eyes, nose, throat and skin. It also has effects on the nervous system.

The OSHA PEL for Stoddard solvent is 500 ppm, but NIOSH recommends that the limit be even lower at 60 ppm.

Dry cleaning Solvent Exposure Levels in Shops Today

Today exposure levels in dry-cleaning shops are much less than they were 30 or 40 years ago. If you still work at a dry-cleaning shop, how you do your work and engineering controls can reduce your exposure.

You Can Protect Your Health

When you visit your doctor or other health care provider, please show him or her this information about the study. He or she will discuss with you any medical screening tests which may be beneficial to you.

Where to get More Information

If you, your doctor, or members of your family have any questions, please the NIOSH toll-free telephone number: 1-800-356-4674. Call between 8:00 a.m. and 4:00 p.m., Monday through Friday, Eastern time.

If you would like copies of the NIOSH study reports on workplace exposure to dry cleaning solvents, please ask.

To contact CDC, please call: 1-800-311-3435

CDC Cancer Prevention and Control: 888-842-6355

To request a copy of the NIOSH study reports on perchloroethylene exposure among dry cleaners, please contact the NIOSH Publications Office at (513) 533-8573.

You may contact the NIOSH Publications Office by e-mail at: pubstaft@cdc.gov.

In addition, you can read the study reports by visiting the following NIOSH web site: http://www.cdc.gov/niosh/.

Once at this site, click on “Safety and Health Topics”. Select the topic “Organic Solvents” to view the reports. The NIOSH Internet web link which will contain more information about work in the dry cleaning industry is now under construction. That link should be added to the list of health topics in the next few months. At that time, you will be able to get more information about perc and other dry cleaning solvent exposures.

For more information on cancer you may contact:

The American Cancer Society


(That’s 1-800-227-4235).


For more information on cervical cancer, please contact:

The U.S. Centers for Disease Control and Prevention (CDC) National Breast and Cervical Cancer Early Detection Program at:


Environmental Concerns

Not only is perchloroethylene bad for your health—it’s bad for the environment too! Read more about the environmental impact of perchloroethylene.