Classification in that category occurs if there is only a suspicion, arising from human and/or animal studies, that a substance or mixture has the potential to cause cancer in humans, but where the evidence is not sufficiently convincing to place that substance in category 1. On the contrary, classification in category 1 requires that it is either known that a substance may cause cancer, based on evidence of causality obtained from human studies between the exposure to that substance and the development of cancer (category 1A) or that it is presumed that the substance has carcinogenic.
