EVERY MONTH OR two, it seems, newspaper headlines proclaim that scientists have discovered a new "cause" of cancer—something that damages cells in a way that makes cancerous changes in the cells' genes more likely. Television news shows, too, carry frightening reports about substances in the environment or lifestyle choices that are said to raise the risk of cancer. Sometimes it appears that, as some people complain, everything causes cancer. Are these reports exaggerated scare stories, or is the danger real"

Cancer from the environment

There is no question that the environment affects a person's chances of getting cancer. All cancer starts because of changes in genes, but most researchers believe that only about 5 to 10 percent of cancers result solely from inherited damage. All the rest arise, at least in part, from mutations that occur during people's lifetimes. Some...