There are certain materials that have been known to cause cancer, and California has made a list of materials that follow into this category.

A big one is PVC. According to my research, there are two different types of PVC: regular PVC, which contain phthalates and supposed phthalates-free PVC. The latter still has some phthalates in it, as one component has just been swapped for another. Companies are claiming them to be free, but please be aware that there is a small amount in them.