Children, the environment and cancer

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Identifying cancer-causing substances


Scientists doing this research typically look at 3 things:



1. How much, how often and under what circumstances people or animals are exposed to a particular substance. Scientists are more confident that exposure is directly related to cancer risk when:
   
   • the risk of cancer increases as exposure increases
   
   
   • the risk of cancer decreases as exposure decreases
     
     
2. How strong and how consistent the relationship is between exposure and the risk of developing cancer. Studies that consistently show the same type of relationship between the exposure and cancer risk are stronger and carry more weight in the decision-making process than studies that show inconsistent results. For example, studies that evaluate the relationship between tobacco use and lung cancer risk consistently show that frequent tobacco users are at much greater risk of developing lung cancer than those who do not use tobacco. 
   
   
3. How similar are the findings in human and animals studies.

After reviewing the scientific evidence, organizations like the World Health Organization and the United States National Toxicology Program draw a conclusion about the risks of cancer associated with exposure to a particular substance.

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