Carcinogen classification systems: similarities and differences

An overview of regulatory classification systems on carcinogens in the Organization for Economic Cooperation and Development (OECD) countries is presented based on a questionnaire study. Most OECD countries have implemented legislation including classification systems and lists of carcinogens. Basically, there are two types of classifications systems. The major difference between the two is that in one system carcinogens are classified according to the weight of evidence for carcinogenic effects in humans, whereas in the other carcinogens are allocated to various groups according to potency. Even if the classification systems may differ, the substances classified as carcinogens are to a large extent the same. Classification of carcinogens will in many countries require hazard labeling. This labeling, i.e., the limit for labeling of substances and preparations, and risk phrases show considerable similarities, but differ in certain aspects. Several countries have restrictions on sale and/or use of carcinogens. There is a trend toward introducing more mechanistic considerations in the classification of carcinogens.