There have been a handful of enormous studies on public health and cell phones, all of which have either found no link, or found a weak link that could also be explained away by those confounding factors we discussed before. But it's on the basis of these studies that the International Agency for Research on Cancer classifies cell phones as "possibly carcinogenic." IARC's designations come up a lot when we talk about things that may cause cancer, mostly because they've listed just about everything as either possibly or probably carcinogenic. To the untrained ear, those classifications make it sound like IARC thinks cell phones pose a small risk to human health. "Possibly carcinogenic" sounds like it's classifying how much cancer cell phones might cause, but really it's classifying whether cell phones cause cancer at all.