The major problem with older type carbon papers is that the carbon might come off easily. This carbon can get into the air and enter inside your lungs if the room is not ventilated. However, in order for this to reach the level of toxicity, you need to be using an incredible number of carbon copies in a room without ventilation. This is a quite unlikely situation, especially these days. Therefore, it is extremely rare for carbon papers to cause toxicity. That being said, you have to be a bit careful when you are handling them. If a lot of carbon gets on your skin, it can lead to itching and irritation.