The short answer
Ethylene oxide is a gas used to sterilize medical devices and make other chemicals. Breathing it, mainly at work or near some facilities, is linked to blood cancers and breast cancer. Emissions controls reduce exposure.
Ethylene oxide is classified as a known human carcinogen (IARC Group 1).
People are mainly exposed by breathing the gas at work or near certain sterilizing facilities.
It is most strongly linked to blood and lymphatic cancers, and breast cancer.
A carcinogen classification describes hazard — whether something can cause cancer — not your personal risk at a given exposure.
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The full explanation.
The simple version
Ethylene oxide is a gas used to sterilize medical equipment that heat would damage, and to make other chemicals. Breathing it over time — mainly workers and some communities near sterilizing plants — is linked to certain blood cancers.
What ethylene oxide is
Ethylene oxide is a colorless, flammable gas. It is widely used to sterilize medical and dental equipment and to manufacture products like antifreeze and detergents. The EPA has taken steps to reduce emissions from sterilizing facilities.
How people are exposed
Common ways people come into contact with it:
- Working in medical-device sterilization or chemical manufacturing
- Living near some commercial sterilizing facilities
- Tobacco smoke contains small amounts
The cancer connection
Ethylene oxide is linked to cancers of the blood and lymph system (such as leukemia, non-Hodgkin lymphoma, and myeloma) and to breast cancer. Evidence is strongest in exposed workers.
The International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, places ethylene oxide in Group 1, carcinogenic to humans — the strongest evidence category, meaning there is enough evidence that it can cause cancer in people. In the United States, the National Toxicology Program's Report on Carcinogens lists it as known to be a human carcinogen.
Hazard is not the same as risk
It helps to separate two ideas that are easy to mix up: hazard and risk. When an agency lists ethylene oxide as a carcinogen, it is making a statement about hazard — whether the substance is capable of causing cancer under some conditions. It is not, by itself, a statement about your personal risk, which depends on how much you are exposed to, for how long, and other factors. Two substances in the same group can carry very different real-world risks. The label answers "can it cause cancer?" — not "how likely is it to cause cancer for me?"
How to lower your exposure
- Rely on workplace exposure limits and emissions controls
- Support EPA measures that reduce facility emissions
- Do not smoke
If you are looking at your overall cancer risk, small, steady steps add up. See our overview of cancer prevention and what raises cancer risk to put any single exposure in context.
The bottom line
Ethylene oxide is a known human carcinogen (IARC Group 1). The most important thing you can do is understand where exposure comes from and take reasonable steps to reduce it, without losing sleep over a single label. Focus your energy on the biggest, most controllable risks in your own life.
Words to know
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Common questions
▸Does ethylene oxide cause cancer?
Yes. Ethylene oxide is classified as a known human carcinogen, which means there is strong evidence it can cause cancer in people. How much any one person's risk rises depends on how much they are exposed to and for how long.
▸How are people exposed to ethylene oxide?
Most exposure happens by breathing the gas at work or near certain sterilizing facilities.
▸Which cancers are linked to ethylene oxide?
It is most strongly linked to blood and lymphatic cancers, and breast cancer.
▸How can I reduce my exposure to ethylene oxide?
The main steps are workplace exposure limits and facility emissions controls.
▸Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether ethylene oxide can cause cancer under some conditions — not a prediction that any one exposed person will develop cancer. Your actual risk depends on the amount and length of exposure and other factors.
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