These two closely related chemicals are added to oil-containing foods to prevent oxidation and retard rancidity. The International Agency for Research on Cancer, part of the World Health Organization, consider BHA to be possibly carcinogenic to humans, and the State of California has listed it as a carcinogen. Some studies show the same cancer causing possibilities for BHT.
BHT and BHA are totally unnecessary. To avoid them read the label. Because of the possibility that BHT and BHA might cause cancer, both should be phased out of our food supply.