Exactly what causes cancer is not yet certain. However, some common causes have been found. The risk of developing cancer usually increases with age , as the body's immune system gradually weakens during this time. It is estimated that 70% of people diagnosed with cancer are over 60 years of age. Researchers have found a strong link between cancer and the diet and lifestyle. For example , smoking or drinking has been linked to cancer of the lungs , mouth and throat, and liver. Similarly, betel nut , jordan , meat , extra salt , sugar, etc. are associated with cancer. Those who generally do less physical activity are also more prone to cancer. Family history has also been found to have a genetic link to cancer. Because of this, if one member of the family has been diagnosed with cancer, the risk of others getting cancer is greatly increased. Environmental and occupational factors Chemicals have a very large relationship with cancer. For example , in mesothelioma (a rare type of cancer that involves cells around the lungs and abdomen), 9 out of 10 people are exposed to asbestos metal. In general, those involved in the shipbuilding industry are more likely to come in contact with the metal. This is why the use of this metal is banned in many countries. Similarly, those who work in paint factories , rubber or gas work are exposed to bladder cancer due to exposure to certain chemicals. The use of these chemicals has since been banned in many countries. One of the environmental factors is the sun. Prolonged exposure to the sun increases the risk of skin cancer. There is also a risk of various cancers due to radioactivity.