ETO sterilization is a method of killing bacteria, viruses, fungi, and spores on medical devices and other products using ethylene oxide gas. It is the sterilization method used on roughly 50 percent of all sterilized medical devices in the United States, making it one of the most important processes in modern healthcare supply chains. The technique exists primarily because many critical medical devices are made from materials that would melt, warp, or break down under the high heat of traditional steam sterilization.
How Ethylene Oxide Kills Microorganisms
Ethylene oxide is a small, highly reactive molecule that penetrates packaging and reaches surfaces that liquids and steam cannot. Once it contacts a microorganism, it works through a chemical process called alkylation: it essentially swaps out hydrogen atoms in the organism’s DNA, RNA, and proteins with bulkier chemical groups. This disrupts the cell’s ability to carry out normal metabolism and reproduce, effectively rendering it dead. Because it attacks multiple biological targets at once, ethylene oxide is considered a broad-spectrum sterilant capable of achieving full sterility, not just partial disinfection.
Why It’s Used Instead of Steam
Steam sterilization (autoclaving) is faster and cheaper, but it requires temperatures above 121°C (250°F). That rules it out for a large category of modern medical devices built from plastics, rubber, certain metals, and electronic components. Endoscopes, catheters, surgical kits with battery-powered elements, and devices with adhesives or coatings all fall into this category. ETO sterilization typically operates between 37°C and 63°C (roughly 99°F to 145°F), which is gentle enough to leave these materials intact while still achieving complete sterility.
The gas also has an advantage in penetration. Complex devices with narrow lumens, multiple layers of packaging, or hard-to-reach internal channels can be difficult to sterilize with methods that rely on direct surface contact. Ethylene oxide, as a gas, diffuses into these spaces more reliably.
The Sterilization Cycle
An ETO sterilization cycle is a multi-phase process that takes considerably longer than steam autoclaving, often spanning several hours to more than a day depending on the load.
- Preconditioning: Products are placed in a controlled environment where temperature and humidity are raised to optimal levels. Moisture is important because it makes microorganisms more vulnerable to the gas.
- Gas exposure: Ethylene oxide is introduced into the sealed sterilization chamber. The gas concentration, temperature, humidity, and exposure time are all tightly controlled. This phase typically lasts one to six hours.
- Aeration: After sterilization, residual ethylene oxide must be removed from the products and packaging. This is the longest phase, sometimes taking 12 hours or more, because ethylene oxide residues left on a device could irritate tissue or cause harm to patients. Mechanical aeration uses repeated cycles of air exchange and heat to drive off the gas.
The total turnaround time, from loading a chamber to releasing a product for use, can range from roughly 15 hours to several days. This is one of the method’s biggest practical drawbacks compared to steam sterilization, which can complete a cycle in under an hour.
What Gets Sterilized With ETO
The list of products sterilized with ethylene oxide is extensive. In healthcare, it covers surgical kits, wound care products, catheters, endoscopes, stents, and devices containing electronics or batteries. Beyond medicine, ETO is used to sterilize certain spices, cosmetics, and animal feed where other methods would degrade the product. Large commercial sterilization facilities process enormous volumes of packaged medical devices before they ever reach a hospital, which is why the method accounts for such a large share of the medical device market.
Health Risks of Ethylene Oxide
Ethylene oxide is classified as a known human carcinogen by both the National Toxicology Program and the International Agency for Research on Cancer (IARC Group 1, its highest classification). Long-term occupational exposure has been linked to increased risk of cancers of the blood and lymphatic system, and possibly breast cancer. Short-term exposure at high levels can cause respiratory irritation, headaches, nausea, and neurological symptoms.
For patients receiving devices sterilized with ETO, the risk is minimal when aeration is performed correctly, because residual gas levels on the finished product are extremely low. The primary concern is for workers inside sterilization facilities and for communities living near them, where emissions from the process can raise ambient air concentrations of the chemical.
OSHA sets the permissible exposure limit for workers at 1 part per million averaged over an eight-hour shift. Facilities are required to monitor air levels, provide protective equipment, and implement engineering controls to keep exposure below that threshold.
Regulatory Pressure and Emissions
The tension around ETO sterilization sits at the intersection of two realities: the healthcare system depends on it for half its sterilized devices, and the chemical it uses is a confirmed carcinogen with environmental consequences. The EPA finalized rules in 2024 requiring commercial sterilization facilities to significantly reduce ethylene oxide emissions, with compliance deadlines set for 2026 and 2027 depending on the specific standard. However, as of early 2026, the EPA has proposed repealing those rules, citing concerns about the burden on sterilization facilities and the potential disruption to the medical supply chain.
This regulatory uncertainty reflects a broader debate. Environmental and public health advocates push for tighter controls on emissions, while the medical device industry warns that overly aggressive regulation could create shortages of sterile devices. Some facilities have already invested in emission-capture technologies that destroy ethylene oxide before it leaves the building, but retrofitting older plants is expensive and time-consuming.
Alternatives to ETO Sterilization
Several alternative low-temperature sterilization methods exist, though none has fully replaced ethylene oxide at scale. Hydrogen peroxide plasma sterilization works well for many heat-sensitive devices but struggles with long, narrow channels and cannot penetrate certain packaging materials. Nitrogen dioxide and supercritical carbon dioxide sterilization are newer approaches under development. Radiation sterilization using gamma rays or electron beams is effective for some products but can degrade certain plastics and is not suitable for electronics.
Each alternative has trade-offs in terms of material compatibility, penetration ability, cycle time, and cost. For now, ethylene oxide remains the only method validated for the full range of complex, heat-sensitive medical devices that modern medicine relies on, which is why it continues to dominate despite the health and environmental concerns surrounding it.