If such people also smoke, this makes the risk of cancer even greater. Carcinogens are substances which can start the process of cancer. Tobacco smoke contains carcinogens which cause lung cancer. Foods may contain carcinogens. However, the risk from carcinogens in foods is low because if they are present, it is usually in very small amounts.
Aflatoxins are examples of carcinogens in foods.
An example of these substances is those produced in peanuts that are contaminated by the growth of moulds. A large proportion of cancers are influenced by environmental factors. This is known because research has been done to compare the most common types of cancers in different groups of people. These types of studies do not show that a particular factor causes cancer, but they suggest links between aspects of lifestyle and cancer. These links are often examined in more detail by studying people with cancer.