BHA and BHT are synthetic antioxidants used to prevent fat rancidity in pet food, particularly in dry kibble. The FDA permits both as food additives, but BHA is classified as "reasonably anticipated to be a human carcinogen" by the US National Toxicology Program based on animal studies. Many premium brands have switched to natural antioxidants (mixed tocopherols, rosemary extract, vitamin E). Their presence is not a definitive harm signal but is a notable ingredient quality differentiator.