How safe is ethylene oxide for medical sterilization?

Michael L. Dourson, Ph.D., DABT, FATS, FSRA

At one or more times in our lives, we are all likely to find ourselves in a doctor’s office or hospital for a medical procedure. Or we can decide to donate blood so that someone else’s life can be improved or even saved. Often, medical personnel use equipment to monitor our symptoms or to take action. Sometimes this equipment is used only once, like gloves, but often it is reused, like stethoscopes or scalpels.

So how does the medical community keep this equipment free of contaminating bacteria, viruses and fungi? By sterilization! All various medical tools or equipment used in medical offices or hospitals are routinely sterilized, either by wiping surfaces with disinfectants, reusing medical tools after being heated to a level that kills these organisms, or not using equipment only once. All of these processes work and play an important role in our security. However, even single-use equipment must be sterilized beforehand. So how does this happen?

Sherry Wade, one of two Sterile Processing Technicians at the Boak Dental Clinic, is responsible for the sterilization, cleaning, processing, assembly, storage and distribution of medical supplies.

There are several ways to sterilize single-use medical equipment, such as using radiation, heat, or a disinfectant chemical such as ethylene oxide. Each of these means has advantages and disadvantages. For example, the plastic tubes that are used to deliver blood and saline solution to many of us cannot be sterilized by heat or radiation because that would usually melt the plastic. In such cases, ethylene oxide is used because it is dry, penetrates the openings in the plastic, and leaves little or no residue. In other words, ethylene oxide and similar disinfectants are invaluable tools for keeping people safe and protecting them from infections caused by potentially unsanitary medical equipment.

Ethylene oxide is produced in the human body

As you can imagine, using disinfection also carries a risk (just like not using disinfection carries a risk). In the case of ethylene oxide, the risk is the development of cancer, but only at very high exposures, well beyond what you could get with hospital equipment. As I’ve said before, government agencies work very hard to develop safe levels for chemicals like ethylene oxide – that is, levels that will cause little or no cancer, but that would still allow use for medical sterilization. Unsurprisingly, the US Environmental Protection Agency (EPA) developed a safe level of ethylene oxide in 2016 which I reviewed for them. However, many people are now re-examining this EPA value because new information shows that our bodies actually make a small amount of ethylene oxide each day, just from normal metabolism. Ripening fruits also emit ethylene gas, a small amount that our bodies convert into ethylene oxide. Fortunately, these amounts are well below any level that can cause cancer.

This new knowledge suggests that the old level of EPA was too safe (not a bad thing), but using it now suggests that we are getting more cases of a specific type of cancer than we actually are. found in our population. A more recent government assessment by the Texas Commission for Environmental Quality analyzed this new knowledge and proposed a much higher level of safety than the EPA. Texas value is always safe and consistent with what our bodies make every day. Other groups, such as the US Food and Drug Administration, have also looked at this new knowledge and come to roughly the same conclusions as Texas.

An understandable misunderstanding

Due to these differing estimates of safety levels and the intense need for medical sterilization during the COVID pandemic, ethylene oxide has been in the news. Its use in medical device sterilization facilities has often been erroneously considered a threat to public health due to the discovery of cancers at very high exposures. In part, this misunderstanding is understandable, especially in light of the old EPA assessment that we now know did not fully account for our body’s production of ethylene oxide or its prevalence. into the environment from many other sources.

So, will the EPA use this additional information and change its level of safety? May be.

The EPA could easily say that their old assessment was the best they could do at the time (I reviewed it for them, so it’s true), correctly say that new data has since been released, and then declare that Texas has done a good job of standing on its shoulders and taking the next step towards a more scientifically accurate but still safe level of EtO exposure.

But if the EPA doesn’t, we know: ethylene oxide does a great job of cleaning medical equipment; our bodies manufacture it daily at levels well above the old EPA safe level; and we are exposed to it at natural levels from sources other than medical sterilization factories. Moreover, the pandemic has shown us how important the need for sterilized medical equipment is. Nor is it reasonable to label human breath as hazardous as a Superfund waste site, which is the practical implication of continuing to use the old EPA safety level.

Michael Dourson is a local board-certified toxicologist and scientific director of the nonprofit organization Toxicology Excellence for Risk Assessment (, which studies chemical risks for government and industry. He is also president of the non-profit Toxicology Education Foundation (, which helps the public understand toxicology concepts and specific information about chemicals, and serves as a science advisor for the website of the American Council on Science and Health ( Questions from readers are welcome. Send them to [email protected]

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