Cancer causes

Damage to our DNA happens by chance and as we get older more of our DNA becomes damaged. This is why cancer is more common in older people.

Around three-quarters of cancer cases occur in people aged 60 and over.

Some of this damage is unavoidable, but we can also harm our DNA by the things we do, like smoking or lying out in the sun. The name carcinogen is given to any substance that causes damage that may lead to cancer. So the chemicals in cigarettes or the UV radiation from the sun are both types of carcinogen.

Our chances of getting cancer may also be increased because we have had a particular type of infection or because of a faulty gene that is passed on from one of our parents.

Sometimes DNA damage is caused by an infection with a virus. A virus causes disease by inserting its DNA into the DNA of the person that it has infected. Viruses cause a whole range of diseases from the common cold to AIDS.

• A virus called HPV causes cervical cancer. It is passed on by having sex with an infected person.
• Cancer in some young children, especially those living in Africa, is caused by a virus called Epstein Barr Virus, or EBV.
• The Hepatitis B virus can cause liver cancer.
• People with AIDS are more likely to get some types of cancer.

Sometimes infection can be caused by a bacterium. Most cases of stomach cancer are caused by infection with a bacterium called Helicobacter pylori. The infection can cause cell changes that may lead to cancer.

Our DNA is passed on, or inherited, from our parents. A small number of people develop cancer because one of their parents has passed on a faulty gene to them. Inheriting a faulty gene does not mean that you will get cancer - but it does mean that you may be more likely to get cancer. In families where cancer is very common, doctors make sure that members of the family are closely monitored for signs of cancer.

Some people's jobs put them at greater risk of cancer because they deal with harmful substances that may cause DNA damage.

In the past people did not realise that some chemicals used in industry can cause cancer. Asbestos dust is known to cause lung cancer and so its use is no longer allowed. In factories and work places where dangerous chemicals are still used all workers have to wear protective clothing and follow safety guidelines.

Image of cancer cells kindly provided by the EM Unit at the London Research Institute.