Acrylamide, a chemical linked to cancer in animal studies, forms in certain foods cooked at very high temperatures, including toast. The FDA has warned that acrylamide is likely to cause cancer in humans, notes AARP.
Acrylamide tends to develop when sugars in food are exposed to a sufficient level of heat as to cause browning. To avoid unnecessary exposure to acrylamide, AARP recommends eating light-brown toast, as darker toast contains more of the chemical.
As of 2013, some evidence suggests that acrylamide may increase risks for endometrial and ovarian cancer, according to epidemiologist Kathryn Wilson via AARP. No link has been found between acrylamide and breast or prostate cancer.