What causes cancer?

Cancer typically occurs when cells in a part of the body become abnormal, and keep on dividing to make more abnormal cells. (For more on this, see the article )¹ It is caused by changes to genes that control how cells grow; these changes may include mutations, which can be inherited or acquired.²

Lifestyle behaviours such as the following can increase your risk:

Excessive alcohol consumption:
- More than 1 alcoholic drink per day for females and more than 2 alcoholic drinks per day for males^3,4,5
One drink is 148 mL of wine or 355 mL of beer or 44 mL of spirits⁵

Unhealthy diet:
- Eating a lot of processed or red meat can increase the risk of certain cancers⁶
- A high-salt diet may also be linked to an increased risk of certain cancers⁶
Smoking³
Too much exposure to sunlight or UV radiation, e.g. due to sunbathing^3,7

Changes may also be brought about by exposure to environmental risk factors such as:

Exposure to cancer-causing substances (e.g. asbestos)^3,8
Exposure to high-energy radiation
- For example from a nuclear power plant or from atomic weapon testing^3,9

Some physical conditions may make you more prone to cancer, for instance:

Hormones
- Increased exposure to high levels of oestrogen and progesterone, e.g. if you start your periods early or have a late menopause, or you had your first full-term pregnancy at a late age, has been linked to an increased risk of breast cancer^3,10,11
Infection
- Certain viruses may increase your risk of cervical cancer. For example, certain types of human papillomavirus (HPV) may increase your risk of cervical cancer^3,12
Obesity³
Obesity is defined as a body mass index (BMI) of 30 or above¹³

Mutations in genes that are passed down through families can increase your risk of developing certain cancers.¹⁴

Your risk is determined by a complex combination of genetics, environmental factors, and lifestyle factors.¹⁵ This can explain why some people with several risk factors never develop cancer, while others with no known risk factors do develop cancer.¹⁴

Glossary

References