When most people think of the word "environment," they think of forests, oceans, or mountains.
In cancer research, however, scientists define the environment as everything outside the body that
enters and interacts with it. This interaction is called an exposure. So, environmental exposures
can include such factors as sunshine, radiation, hormones, viruses, bacteria, and chemicals in the
air, water, food, and workplace, as well as lifestyle choices like cigarette smoking, excessive
alcohol consumption (more than 2 drinks/day), an unhealthful diet, lack of exercise, or sexual
behavior that increases one's exposure.
Researchers have estimated that as many as 2 in 3 cases of cancer (67 percent) are linked to some
type of environmental factor, including use--or abuse--of tobacco, alcohol, and food, as well as
exposures to radiation, infectious agents, and substances in the air, water, and soil.
![What Is the Environment?](https://webarchive.library.unt.edu/eot2008/20080920101927im_/http://www.cancer.gov/images/Documents/167a5f6c-1c75-4b8a-b1bc-c7520def8d6b/slide2.jpg)
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