Ethylene oxide is used to sterilize surgical instruments. It can also be a contaminant of personal care products such as shampoos and body washes, because it is used to buffer the harshness of some sudsing agents, and trace amounts can be left behind. It is classified as a known human carcinogen and is one of 51 chemicals that the National Toxicology Program (NTP) identifies as mammary carcinogens in animals.