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What causes Cancer?


Our current understanding of what causes cancer is not complete. Although being chronically infected with certain viruses may increase the risk of some types of cancer, cancer is not contagious; no one can catch cancer from another person.

Cancer develops gradually as a result of a complex mix of factors related to environment, lifestyle and heredity. Scientists estimate that 80% of all cancers are related to the use of tobacco products, what we eat and drink, and to a lesser extent, cancer-causing agents (carcinogens) in the environment and workplace. Some people are more sensitive than others to factors that can cause cancer due to inherited predisposition.

 Keep in mind that not everyone with a risk factor will get cancer. Most people do not.

Some factors known to increase the risk of cancer:


Tobacco causes cancer. Smoking tobacco, using smokeless tobacco, being regularly exposed to environmental tobacco smoke causes up to one-third of all cancer deaths. Smoking accounts for more than 90% of all lung cancer deaths. If you smoke, your risk of lung cancer is affected by the number and type of cigarettes ('low-tar' cigarettes are not protective) you smoke and how long you have been smoking. Smokers are more likely than non-smokers to develop larynx, esophagus, pancreas, bladder, kidney, cervix and lung cancers. The risk begins to decrease as soon as a smoker quits. Chewing tobacco can also cause cancers of the mouth and throat. Exposure to environmental smoke increases the risk of lung cancer. The relative risk of cancer goes up by 30% for a non-smoking spouse of a smoker and possibly also for the children.

As smoking is one of the main contributory factors of cancer, the best way to minimize the risk of developing cancer will be to dissociate from smoking. The following are useful links for individuals who wish to embark on smoking cessation journey:


 The choice of food may affect the chance of developing cancer. There is a link between a high-fat diet and certain cancers, such as cancer of the breast, colon, uterus, and prostate. Being overweight is linked to increased rates of cancers of the prostate, pancreas, uterus, colon, and ovary. On the other hand, foods such as fruits, vegetables, whole-grain breads and cereals, may help to protect against some types of cancer.


Drinking large amounts of alcohol increases the risk of cancer of the mouth, throat, oesophagus and larynx (voice box). People who smoke and drink have a higher risk of developing cancer than a person who smokes but does not drink. Alcohol can damage the liver and increase the risk of liver cancer.

Environmental Chemicals

Being exposed to chemicals such as asbestos, nickel, cadmium, uranium, radon, vinyl chloride, benzidene, and benzene can increase the risk of cancer. It is important to follow safety and work rules to avoid contact with dangerous materials.

Ultraviolet Radiation

Excessive exposure to sunlight without protection can cause skin cancer.

Infectious Agents

Chronic infection with Human Papilloma virus (HPV), Hepatitis B / C viruses, Epstein Barr virus and Helicobacter Pylori bacteria increase the risks of cervical, liver, nasopharyngeal and stomach cancers respectively.

Family History Of Cancer

A small number of cancers such as melanoma (skin cancer), breast, ovary and colon cancers tend to occur more often in some families than in the rest of the population.

For further enquiries on the causes of cancer, please call the Cancer Helpline at (65) 6225 5655 or email to