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Dose and exposure time

In humans, a single dose of carcinogen is rarely sufficient to cause cancer.
The atomic bombs exploded over Japan led to only a very slight increase in incidence of most cancers in survivors. (An exception was leukaemia in children.) The same applies to survivors of nuclear accidents.

The three clearest examples of cancer caused by particular agents are:

  • Smoking and lung cancer (it takes about 2 million cigarettes to induce one cancer - or 4 million in Japan!)
  • Aflatoxin and liver cancer
  • Ultraviolet and skin cancer

These all involve prolonged exposure.


In a recent investigation of germline mutations caused by radiation Jeffreys and colleagues, they were seen after chronic exposure (e.g. in a population living near a nuclear test site) but not after acute radiation (e.g. radiotherapy after testicular cancer).