Ethylene oxide is a colorless, flammable gas used primarily to manufacture everyday chemicals and to sterilize medical equipment. Its chemical formula is C₂H₄O, and it has a faintly sweet, ether-like odor. Despite being essential to several industries, it is classified as a human carcinogen by the EPA, which has made it one of the most closely regulated industrial chemicals in the United States.
Basic Properties
Ethylene oxide boils at just 10.6°C (about 51°F), meaning it transitions from liquid to gas near room temperature. That low boiling point is part of what makes it useful: as a gas, it can penetrate packaging, tubing, and other hard-to-reach spaces. It is highly flammable, with a flash point below 0°F, so facilities that handle it operate under strict safety controls.
How It’s Used in Industry
The vast majority of ethylene oxide produced in the U.S. never touches a hospital or a spice jar. It serves as a chemical building block, reacting with other substances to create antifreeze, textiles, plastics, detergents, and adhesives. These downstream products are so common that ethylene oxide ranks among the most produced organic chemicals in the world.
Its second major role is sterilization. About 50 percent of all sterile medical devices in the U.S. are sterilized with ethylene oxide. Devices made from certain plastics, metals, or glass, and those with complex shapes or multiple layers of packaging (catheters, stents, wound dressings) often cannot withstand high-temperature steam or radiation. Ethylene oxide gas can reach every surface of these devices without damaging them, then be cleared away before the product ships.
Ethylene oxide is also used to sterilize some food products, including spices, dried herbs, dried vegetables, sesame seeds, and walnuts. This kills bacteria and mold that can survive in dry goods. However, residues left on food have triggered recalls in multiple countries. In early 2024, for example, regulators in Hong Kong recalled packaged chili powder, ground nutmeg, and basil leaves from U.S. brands after testing detected ethylene oxide residues.
Cancer Risk and Long-Term Health Effects
The EPA has concluded that ethylene oxide is carcinogenic to humans through inhalation. The agency’s assessment found that exposure increases the risk of cancers of the lymphatic system and, in women, breast cancer. Those findings come from studies of workers in facilities that manufacture or use the chemical. Animal studies have linked inhalation exposure to tumors in the brain, lungs, connective tissue, uterus, and mammary glands.
What makes ethylene oxide particularly concerning is its mechanism. The EPA concluded that it causes cancer through a mutagenic mode of action, meaning it directly damages DNA. That distinction matters because mutagens don’t have a “safe” threshold in the way some other toxins do. Even low-level, long-term exposure raises concern, which is why communities near sterilization plants and chemical facilities have pushed for tighter emission limits.
What Short-Term Exposure Feels Like
At high concentrations, typically above 260 parts per million where the gas becomes detectable by smell, ethylene oxide causes a range of immediate symptoms. The most common are neurological: headaches, dizziness, nausea, fatigue, muscle weakness, numbness, and memory problems. Respiratory irritation is also typical, including coughing, shortness of breath, wheezing, and nasal irritation.
Other reported effects include excessive thirst and dry mouth, vomiting, diarrhea, stomach cramps, eye irritation, and skin rashes. The gastrointestinal symptoms are actually secondary effects of neurotoxicity rather than direct damage to the digestive system. In severe cases, prolonged high-level exposure can cause lasting nerve damage.
Workplace and Environmental Regulations
OSHA sets the permissible workplace exposure at 1 part per million averaged over an eight-hour shift, with a short-term ceiling of 5 ppm for any 15-minute period. Employers are required to take action once airborne levels reach 0.5 ppm.
On the environmental side, the EPA has been steadily tightening rules. In March 2024, the agency finalized amendments to emission standards for commercial sterilization facilities, requiring changes that will reduce the amount of ethylene oxide released from these operations by 90 percent. A month later, the EPA announced additional rules targeting chemical plants that produce ethylene oxide and other toxic air pollutants. In January 2025, the agency released interim pesticide risk reduction requirements specifically aimed at protecting workers who use the gas for sterilization and people who live, work, or attend school near those facilities.
Why It Hasn’t Been Replaced
Given the health risks, a reasonable question is why hospitals and manufacturers still rely on ethylene oxide at all. The answer is that no single alternative works as broadly. Heat-sensitive plastics warp under steam sterilization. Radiation can degrade certain polymers, changing their strength or flexibility. Ethylene oxide remains the only proven method that can sterilize a wide range of materials without altering their chemical or physical properties.
The FDA has been actively seeking replacements through innovation challenges. Technologies under evaluation include supercritical carbon dioxide sterilization, nitrogen dioxide sterilization, accelerator-based radiation, and vaporized hydrogen peroxide (sometimes combined with ozone). Each shows promise for specific device categories, but none yet matches ethylene oxide’s versatility across the full spectrum of materials and device designs currently on the market. Until one or more of these alternatives can be validated for broad use, ethylene oxide will remain a critical, if controversial, part of the medical supply chain.