Carcinogens also have been found in 49 percent of the prescription drugs that have been tested. Although Ames developed the test for potential carcinogens, he is now concerned that results from cancer tests that apply high doses to animals are misleading and that cancer scare stories cause people to avoid items ranging from apples to soft drinks. Unbalanced diets account for about one-third of cancer cases. Reproductive hormones contribute to as much as 20 percent of all cancer. Lack of exercise, obesity and alcohol intake influence hormone levels and increase risk.
Chronic infections cause about nine percent of cancer cases, mostly in developing countries.
Cancer is also due in part to normal aging. The study rebuts some common misconceptions. For example, human exposure to carcinogenic pesticides is minuscule compared with the background of exposure to carcinogens produced by nature, some of them produced by plants themselves to protect against fungi, insects and animal predators. The study also argues that reducing the use of synthetic pesticides may do more harm than good. Organic fruits and vegetables are more expensive, and higher prices may cause people to buy less produce.