E321 - Butylated hydroxytoluene

Antioxidants stop fats and oils oxidising, which is what gives them off flavours and rancid smells. Some are nutrients in their own right (vitamin C is E300, vitamin E is E306). Others are synthetic phenolic compounds (BHA is E320, BHT is E321) used in dry foods like cereals and crisps where they are very effective at very low doses. The synthetic phenolics are the antioxidants worth knowing about: BHA is classified by the World Health Organisation as possibly carcinogenic to humans, and the US National Toxicology Program lists it as reasonably anticipated to be a human carcinogen.