Ethylene Oxide (ETO): Properties, Mode of action and uses

Ethylene oxide (ETO) has been widely used as a low-temperature sterilant. ETO is a colorless gas that is flammable and explosive but it is liquid at temperatures below 10.8oC.

ETO is an effective sterilizing agent for heat- and moisture sensitive materials in hospitals, industry, and laboratories. Bacterial spore show little resistance to destruction by this agent. It is effective at relatively low temperatures and does not damage materials exposed to it.

It has high penetrating power and passes through and sterilizes large packages of materials, bundles of cloth, and even certain plastics.

Mode of action: Alkylation reactions with organic compounds such as enzymes (eg inactivation of enzymes having sulfhydryl group) and other proteins.

Uses: It is used to sterilize spices, biological preparations, soil, plastics, certain medical preparations and contaminated laboratory equipment.


The main disadvantages associated with ETO are

  1. Its comparatively slow action up on microorganisms. ETO is not used often because it requires a lengthy processing and aeration time (e.g., 12 hours).
  2. Higher cost
  3. Sterilization chamber is small
  4. ETO mixed with air at a ratio of at least 3% EtO gas, forms an explosive mixture. ETO cartridges should be stored in flammable liquid–storage cabinet.
  5. Potential hazards to patients and staff (occupational hazards). ETO should be considered a known human carcinogen. Acute exposure to ETO may result in irritation and central nervous system depression. Chronic inhalation has been linked to the formation of cataracts, cognitive impairment, neurologic dysfunction etc. Occupational exposure in healthcare facilities has been linked to hematologic changes, increaased risk of spontaneous abortions and various cancers.
  6. ETO is absorbed by many materials. For this reason, following sterilization the item must
    undergo aeration to remove residual ETO.


  1. Compatible with most medical materials. It can sterilize heat- or moisture sensitive medical equipment without deleterious effects on the material used in the medical devices.
  2. Equipment is simple to operate and monitor
  3. Penetrates packaging materials and device lumens
  4. Single-dose cartridge and negative-pressure chamber minimizes the potential for gas leak and ETO exposure

Further Reading:

  1. CDC: Guideline for Disinfection and Sterilization in Healthcare Facilities