<unk> s are substances added to<unk>  to preserve flavor or enhance its taste and appearance.
Some<unk> s have been used for centuries; for example, preserving<unk>  by pickling (with vinegar), salting, as with bacon, preserving sweets or using sulfur dioxide as with wines. With the advent of processed<unk> s in the second half of the twentieth century, many more<unk> s have been introduced, of both natural and artificial origin.
Food additive
Inhalant
Designer drug
Hazardous drugs
Generic drug
Cathartic
Toxic metal
Pesticide