If you are not careful, there are a lot of dangers that can arise because of canning tomatoes. Since tomatoes are raw and organic, they can rot and develop mold over time if left out. They do not have a long shelf life, but can be preserved if you freeze them or boil them in airtight sealable containers. The dangers of canning tomatoes include leaving too much air, and using a container with defects. If too much air gets inside the can then there is a possibility that mold and other bacteria will get in. If you eat the tomatoes without knowing you can suffer from stomach pain or food poisoning.