Additives may be natural, nature identical or artificial. Natural additives are substances found naturally in a foodstuff and are extracted from one food to be used in another. For example, beetroot juice with its bright purple colour can be used to colour other foods such as sweets.
Chemicals that are intrinsic constituents of foods, such as hydrazines in mushrooms, may also be carcinogenic. Certain unavoidable contaminants in foods, such as aflatoxin B 1 and polychlorinated biphenyls, have been found to be carcinogenic in long-term toxicological studies.