On 7 April 2023, the California Office of Environmental Health Hazard Assessment (OEHHA) proposed lowering the "No Significant Risk Level" (NSRL) for ethylene oxide under the Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65 (Prop 65).  It was proposed to reduce the NSRL from 2 to 0.058 micrograms per day. Ethylene oxide has been identified as a known carcinogen under Proposition 65. The proposal is open for comments until May 23, 2023. 

Prop 65 requires the inclusion of warning statements when a company's product causes "exposure" to carcinogens or reproductive toxicants. There is no requirement for warnings when exposure is protected by the "safe harbour." The safe harbour for carcinogens is the "No Significant Risk Level" (NSRL), or the level of exposure that would cause no more than one additional case of cancer in a population of 100,000 exposed people, assuming exposure throughout a lifespan of 70 years.