PEG compounds often contain small amounts of ethylene oxide. Ethylene oxide (found in PEG-4, PEG-7, PEG4-dilaurate, and PEG 100) is highly toxic — even in small doses — and was used in World War I nerve gas. Exposure to ethylene glycol during its production, processing and clinical use has been linked to increased incidents of leukemia as well as several types of cancer.