There is no one cause of cancer, but scientists have identified a number of factors that can increase (risk factors) or decrease (protective factors) the chances of getting cancer.
Ionising radiation such as X-rays and radiation given off by radioactive materials can cause chemical changes that can damage the DNA in cells. In cancerous cells, this damage can lead to the death of the cell, but healthy cells have mechanisms to repair DNA damage from radiation. Sometimes, the repair is not perfect and the cell can end up with a mutation that can lead to cancer.
Ultraviolet light, even though it is not ionising radiation, can be pretty nasty to DNA as well, and this damage can lead to skin cancer. Melanin, the pigment in skin, stops UV from penetrating the skin, so people with darker skins have a lower chance of developing skin cancer. Ultraviolet light can also have beneficial effects – it is needed for the production of Vitamin D in the skin, which can protect against cancer. Many of our ancestors came from Europe, where there were low levels of ultraviolet light, and evolved lighter coloured skin as a result. In New Zealand, the UV levels are much higher and, as a result, we have the highest level of skin cancer in the world.
Exposure to different chemicals can increase your risk of cancer. For example, exposure to the chemicals in tobacco smoke is a major risk factor for the development of lung cancer. Alcohol consumption can also increase the risk of some cancers – heavy drinking will increase your risk of getting cancer of the mouth, throat, oesophagus, larynx or liver, and even moderate drinking will increase your risk of getting breast cancer. Exposure to asbestos fibres – a material that was used in buildings to protect them against fire – can lead to a serious lung cancer called mesothelioma.
Some people carry genes that make cancer a lot more likely. Recently, scientists have identified specific genes responsible for certain types of cancer, such as the BRCA genes for breast cancer. If you have had a close relative develop cancer, statistically, you are at a higher risk of developing cancer in the future.
Certain viruses can increase your risk of getting cancer. One of these is the human papilloma virus, which can lead to cervical cancer. Cervical cancer is linked to sexual activity, which can lead to the spread of the papilloma virus. Safe sex precautions such as the use of condoms can reduce the spread of this virus.
Food can both protect you from cancer and increase your risk; it all depends on what you eat. There are naturally occurring chemicals in fruit and vegetables that protect you from cancer, which is one of the reasons why scientists recommend that you have a least five servings of fruit and vegetables per day. Food can protect in other ways, for example, having a diet high in fibre makes it easier for food to move through your digestive system, decreasing the risk of colon cancer. On the other hand, having a diet high in fat increases your risk of getting cancer because some chemicals attach to fat molecules, and they tend to stay in your body longer or remain in cells with the fat as deposits.