Onions contain quercetin, a type of plant chemical called a flavonoid. Some flavonoids have antiproliferative properties—that is, the ability to block the growth of cells. Recognizing the importance of this kind of molecule, researchers at the University of Guelph conducted a study with five types of onions grown in Ontario. It was found that chemicals from the onions killed colon and breast cancer cells, by stimulating the pathways that lead to cell death (apoptosis). The onion extracts were also found to inhibit the growth of these types of cancer cells. Encouraged by the cancer-fighting properties of the onion flavonoids, the researchers developed a safe new method for purifying the chemicals from onions. The ultimate goal is to create food additives and/or supplements from the cancer-fighting chemicals.