There are no known ways to prevent ALL.
A few factors may increase a person's risk of developing ALL, but most are not avoidable. These include:
Exposure to high levels of radiation, such as that from an atomic bomb.
Exposure to certain chemicals, including past treatment with some chemotherapy drugs.
Certain inherited disorders, such as Down syndrome or Fanconi anemia.
Having one or more of these risk factors does not mean you will develop ALL. Many people with the disease do not have any risk factors.