All cancers are caused by abnormalities (mutations) in the DNA of cells in the body. The body has defences against some mutations, but outside agents – such as the cancer-causing chemicals in tobacco smoke, as well as radiation and some infections – can overwhelm these defences. Sometimes the internal nutritional state of the body and the hormones produced in the body can also make these genetic abnormalities more likely to occur.
The main cause of cancer in the European Union is smoking. Overweight or obesity, poor diet, lack of physical activity, and alcohol consumption contribute to unhealthy lifestyle as another major cause of cancer. Sun exposure and some other sources of radiation (e.g. from radon) are also important, as well as exposure to carcinogens in the workplace and certain infections.
For any of these factors, the more that people are exposed (by duration, frequency, and level of exposure), the higher the risk of developing cancer.