Ethylene Oxide: A New Wave of Litigation

Ethylene oxide (EtO) is a naturally occurring gaseous chemical that is used primarily in the production of ethylene glycol for antifreeze and polyester (Agency for Toxic Substances and Disease Registry (ATSDR) 1999). EtO is also used as a sterilizing agent in medical and pharmaceutical applications. It is a potent alkylating agent, and it can disrupt DNA and proteins, making it highly effective at inactivating bacteria, viruses and fungi (Rutala and Weber 2023). Ethylene oxide is essential for sterilizing approximately 50% of all sterile medical devices in the United States, including many products such as plastics, electronics, and delicate pharmaceutical components that cannot withstand high-temperature steam sterilization (Rutala and Weber 2023).  

EtO sterilization has recently drawn attention due to claims and subsequent litigation relating to the development of cancer and other health effects in individuals who live or work near facilities that emit EtO. For example, recent litigation has alleged that medical sterilizer manufacturer was responsible for the release of EtO emissions leading to the development of breast cancer in one plaintiff. Subsequently, over 950 EtO-related claims were settled. Other EtO-emitting facilities have faced similar litigation. Nearly 100 facilities across the country use the compound, suggesting EtO-related claims are likely to increase in the coming years (Turner 2023).  

Regulation and Epidemiology 

EPA regulates ethylene oxide as a hazardous air pollutant under the Clean Air Act and has classified it as a Group 1 carcinogen (U.S. Environment Protection Agency (EPA) 2025). In 2016, the EPA updated its risk assessment for EtO, significantly increasing its inhalation unit risk estimate, making it roughly 50 times more potent than previous estimates (U.S. Environmental Protection Agency (EPA) 2016). The agency established a 1-in-1 million excess cancer risk level at just 0.1 parts per trillion (ppt), meaning that exposure to this concentration over a lifetime could theoretically result in one additional cancer case per million people (U.S. Environmental Protection Agency (EPA) 2016). This level is far lower than background air levels across the U.S., which typically hover between 0.1 and 0.2 ppb (Kirman et al. 2021). 

Scientific agencies have highlighted two main cancers which may be associated with EtO exposure: breast cancer and lymphohematopoietic cancer (primarily leukemia). IARC relies on these cancers to support their classification of EtO as carcinogenic to humans (Group 1) (International Agency for Research on Cancer (IARC) 1987, 2012). EPA uses the same endpoints for characterizing EtO as “carcinogenic to humans” (U.S. Environmental Protection Agency (EPA) 2016). Of the available epidemiological data, two primary studies have been heavily relied upon: Steenland et al. (2003) and Steenland et al. (2004).  

Steenland et al. (2003) studied breast cancer incidence in a cohort of 7,576 women employed for at least one year and exposed for an average 10.7 years while working in commercial sterilization facilities. The authors concluded that there was no causation of breast cancer due to EtO, and a causal association was weakened due to inconsistencies in exposure-response trends and possible biases. Steenland et al. (2004) is a follow-up to a NIOSH study of 18,235 ethylene oxide-exposed workers at sterilization facilities extended from 1987 through 1998. The authors concluded that there was little evidence of excess cancer mortality for the cohort as a whole. Lynch et al. (2022), a meta-analysis, reviewed epidemiological studies related to EtO and cancer and concluded that there was a lack of clear and consistent evidence linking EtO exposure to the development of cancer.  

Ultimately, although there are claims that EtO causes cancer in individuals working with or living near EtO-emitting sterilization processes, epidemiological evidence does not consistently demonstrate this alleged relationship.