We don’t know what causes most cases of chronic myeloid leukaemia. But there are some factors that may increase your risk of developing it. Having any of these risk factors doesn't mean that you will definitely develop cancer.
If you have had radiotherapy for cancer before, this could increase your risk of developing CML. This risk is very small compared to the benefit of radiotherapy treating the cancer.
Some studies show radiation can increase risk because atomic bomb survivors had an increased risk of leukaemia. There is a 20 year study of the workers who cleaned up after the Chernobyl nuclear power plant accident in 1986. It showed that even at low doses of radiation there is an increased risk of all types of leukaemia.
There is some evidence that lots of contact with the chemical benzene over many years may increase CML risk.
Benzene is one of the chemicals in petrol. It’s also a solvent used in the rubber industry. Most people in the UK wouldn't come into contact with enough benzene for it to increase their risk at all.