Are face masks treated with Ethylene Oxide?

What is Ethylene Oxide?

Ethylene Oxide (ETO) is a man-made, colourless highly flammable gas with a faintly sweet odour. It's used as a fumigant for sterilizing foods and heat-sensitive medical equipment that can not be sterilized by steam (such as face masks). Through a five stage process, ETO efficiently penetrates protective equipment, destroying bacteria and viruses.

How does Ethylene Sterilization Work?

Basic ETO sterilization cycle consists of five stages and takes 2.5 hours. Preconditioning, humidification, gas introduction, exposure, evacuation and air washes. Once this is done, aeration begins for 8-10 hours. Because ETO is absorbed by many materials, aeration is then needed for 8-10 hours at 50-60 degrees to degas (essentially remove) residual ETO so that the material complies with regulatory standards and is safe for us to use.

Concentrations of residual ethylene oxide in medical devices generally decline rapidly after further (a few days’) aeration, although levels exceeding 180mg/L were sometimes measured following aeration. 

Health Implications of Ethylene Oxide

The World Health Organisation and The International Agency for Research on Cancer (IARC) and the US Environmental Protection Authority has classified ethylene oxide as a cancer-causing agent (carcinogen).

Pharmacokinetics data show that ethylene oxide is readily absorbed from the respiratory tract in humans and the CDC link occupational exposure in healthcare facilities to an increased risk of spontaneous abortions and various cancers. Injuries (e.g., tissue burns) to patients have been associated with ETO residues in implants used in surgical proceduresResidual ETO in capillary flow dialysis membranes has been shown to be neurotoxic in vitro.

One study showed that at levels ≥260mg/L ethylene oxide vapors affect the eyes, respiratory tract, central and peripheral nervous systems, gastrointestinal tract (probably secondary effects to nervous system toxicity), hematopoietic system, and possibly the reproductive system and fetus.

Additional studies in animals exposed to ethylene oxide for up to 6 h/day provided evidence of reproductive toxicity (subchronic exposure), developmental toxicity, neurotoxicity, genetic toxicity in germ cells, and carcinogenicity. 


Government Standards for Safety

There are two voluntary consensus standards that describe how to develop, validate, and control ethylene oxide sterilization processes for medical devices and the acceptable levels of residual ethylene oxide and ethylene chlorohydrin left on a device after it has undergone ethylene oxide sterilization. 

ANSI AAMI ISO 11135:2014

ANSI AAMI ISO 10993-7:2008(R)2012

These standards help ensure levels of ethylene oxide left on medical devices are within safe limits.

Within the standards, ETO limits for devices have been established based on how the device is used, how often, and how long in order to pose a minimal risk to patients in normal product use. 

To put things into perspective...

Mainstream tobacco smoke contains 7mg/L ethylene oxide per cigarette. 

The Scientific Committee on Occupational Exposure Limits (SCOEL) states when wearing a face mask for eight hours a day, the exposure of Ethylene Oxide must not exceed 5mg/L.

China’s National Health Commission states exposure to Ethylene Oxide must not exceed 1mg/L.

There is no doubt at all, that wearing a mask greatly reduces transmission of respiratory and other infections.

If you would rather avoid Ethylene Oxide all together, here are some suggestions:

Wear a reusable cloth mask (remember to wash these) 

Find a brand of surgical masks that does not use Ethylene Oxide to sterilise their masks (search their website or email the brand)

We hope this helps clear up some misconceptions floating around the internet around mask wearing, giving you the information needed to make informed decisions best suited to protect you and your loved ones. 

Welcome to the movement, 


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Our biggest challenge in this new century, is to take an idea that seems abstract - sustainable development - and turn it into a reality for all the world's people.

Kofi Annan