What causes cancer?

Published 30 October 2018

Most cancers are not caused by a single event. There are usually several different things that happen over time to damage cells or make them divide more, increasing the chance of them becoming abnormal.

Cell mutations can result in cancer

Usually when cells in the body divide, the new cells are exact copies of the old cells. When this process goes wrong, the new cells are slightly different from the old ones.

This change happens in the genetic material (DNA) inside the cells, and is called a mutation.

While most cells with mutations will die or not cause any problems, a very small number will go on to cause cancers.

What makes cells mutate?

The more often cells divide, the greater the chance of mutations occurring.

Most mutations are spontaneous, with no real reason for the change, however there are certain things that can cause mutations or make cells with mutations more likely to become cancers. These include:

• damage to cell DNA
  • radiation, including ultraviolet radiation from the sun
  • chemicals in tobacco smoke
  • substances produced by the body, called reactive oxygen species
• cells dividing more often
  • getting older, which increases the number of times cells have divided
  • the female hormone oestrogen which stimulates some cells in the breast or womb to divide
• abnormal cells not dying
  • the human papilloma virus can help abnormal cells in certain areas of the body to continue to live and divide. 

What are cancer risk factors?

Things that increase the chance of getting cancers are called risk factors.

Some risk factors can't be changed, like a person's age or family background. Other risk factors can be changed. These are usually called lifestyle risk factors.

Risk factors for cancer include:

• Getting older—many cancers are more common as people get older.
• Family history—some families carry a faulty gene that can be passed on from one generation to the next, with family members who carry the gene having an increased risk of certain cancers.
• Smoking—lung cancer and several other cancers can be caused by chemicals in tobacco smoke.
• Alcohol—excess alcohol use has been linked to a number of different cancers.
• Ultraviolet (UV) radiation—exposure to UV radiation from the sun can cause melanomas, and other skin cancers.

• Some viruses and other organisms—the human papilloma virus (HPV) causes most cases of cervical cancer.

• Being overweight or obese—this can increase the risk of certain cancers.
• Diet and exercise—lack of exercise or an unhealthy diet are thought to increase the risk of some cancers.

Find out more about cancer risk factors in our Prevention section.