Vinyl chloride monomer, the substance from which PVC (polyvinyl chloride) is manufactured, has been shown to cause liver cancer among those working with it. This was due to previously poor hygiene conditions in the manufacturing process. Workers who maintained reaction vessels holding the gas were exposed, increasing their risk of two types of liver cancer. These days, there are more stringent safeguards in place. PVC in home products is a different matter. Such products contain plasticisers such as phthalates that make them softer and more flexible. Some people have claimed that these chemicals can leach out of PVC products, like vinyl flooring or plastic wires, and cause cancers such as breast cancer. However, there is no good evidence that phthalates in PVC products can increase the risk of any type of cancer. When PVC is burned in incinerators or landfill fires, it does release chemicals called dioxins, which can increase the risk of cancer.