Perhaps we are a society that relishes bad news. Or maybe by definition bad news is news. Whatever the explanation, 2004 was full of headlines about modern living allegedly making us sick.

The top 10 health scares of the last 12 months -- described below -- have some common characteristics: some of these reports overlook the basic toxicological principle that "the dose makes the poison" and assume that if a lot of something is bad then a little is risky too; some rely on a single, often unpublished study that means little out of the context of other literature in the field; and many swallow whole the baseless mantra "if it causes cancer in a lab animal, it must be assumed to pose a human cancer risk."

The top 10 unfounded scares for 2004 are:

1. Childhood vaccines cause autism. This claim has been around for a while, but it received enormous press exposure this year, with emphasis on the claim that thimerosal, a vaccine preservative, is the culprit. Coverage ranged from blatant scaremongering and dismissal of scientific evidence to fairly unbiased assessments of the data. The bottom line: to date, all the evidence supports the view that there is no link between thimerosal-containing vaccines and autism, or between any vaccines and autism. This is the conclusion supported by the body of published peer-reviewed scientific studies.

2. Farmed salmon causes cancer. Last year, the Environmental Working Group launched this scare, releasing a study of seven farmed salmon that they said had measurable levels of PCBs -- industrial chemicals. This year, an article in Science presented data showing that farmed salmon had higher levels of PCBs than wild salmon. But the warnings that found their way into the press were exaggerated fears based on the assumption that because PCBs are animal carcinogens they must pose a human cancer risk even at trace levels. Indeed there is no evidence--even at high levels -- that PCBs cause human cancer. Many synthetic and natural chemicals in food cause cancer in high doses in rodents--and those findings have no direct relevance for human cancer risk.

3. Cell phones cause brain tumors. Another oldie-but-goody made a comeback in 2004 when researchers at an institute in Sweden released a study supporting a link between cell phone use and acoustic neuromas. Even the authors pointed out their study was small and had never been replicated. Further, the study involved analog cell phones, not the digital phones that are the vast majority of those used today. But the story was widely covered nonetheless. The mainstream scientific view is that the health effects of using cell phones are negligible.

4. Nightlights cause leukemia. In September 2004, scientists at a conference in Britain suggested that increased light at night (not nightlights specifically) may contribute to leukemia in children. Media reports understandably caused anxiety in parents of young children. But, while the rise in childhood leukemia justifies legitimate research, there is currently no reason to believe that nightlights pose any danger to children (unless, of course, the bulb is really hot or they eat it).

5. Chemicals in cosmetics pose a heath hazard. In June of 2004, the Environmental Working Group released yet another report accusing a variety of cosmetic manufacturers of using ingredients that increase the risk of pregnancy problems or cancer. Once again, this scare was based on the assumption that things that pose cancer in high doses in rodents must pose a risk of human cancer, a claim that has no basis whatsoever in scientific reality.

6. Mercury in seafood threatens health. Mercury is a toxic metal, and at high levels it can indeed pose a serious threat to human health. But again, media reports overlooked the "dose makes the poison" rule. The government has strict tolerance levels for mercury in fish, and at the levels found in fish, mercury does not pose a health hazard to humans.

7. Cheeseburgers cause heart disease. When former President Bill Clinton announced just before Labor Day that he had been diagnosed with severely blocked coronary arteries and needed bypass surgery, the media had a field day blaming his condition on his diet -- particularly his penchant for fast food burgers and fries. Frequent film footage showing the former President in front of McDonald's and Burger King filled the nightly news. While it is true that lifestyle factors such as smoking, inactivity, and obesity can raise the risk of a heart attack, so can a family history of predisposition toward high "bad" cholesterol, low "good" cholesterol, and high blood pressure. For preventing heart disease, medications that control blood pressure and cholesterol levels are more important than avoiding cheeseburgers or any other specific food.

8. Antibiotics cause breast cancer. A flurry of media coverage followed a February article in the Journal of the American Medical Association finding that prescriptions for antibiotics had been more common among women who had been diagnosed with breast cancer. But as an editorial accompanying the article noted, "this study provides many (or more) questions than answers" -- and did little to further our understanding of the causes of breast cancer.

9. Teflon causes health problems. This health scare was a spin-off of some wrangling between Teflon's manufacturer, DuPont, and the EPA, which wanted more data on the presence (in the environment and in blood) of chemicals used in producing Teflon. It really had nothing to do with scientific evidence of harm to health, as some media announced. There is no convincing scientific evidence that the chemical harms human health, nor that it is present in Teflon itself.

10. Soda causes esophageal cancer. Saving the worst for last, this scare came on the scene when scientists from India reported a correlation between a rise in per capita consumption of soda in the U.S. and the occurrence of esophageal cancer--which media interpreted as a causal connection. Since this "study" did not have any scientific findings about cancer risk--simply showing that both soda consumption and esophageal cancer became more prevalent over the same time period -- it is remarkable that the mainstream media even reported it at all.

With a little luck, this round-up of 2004's worst unfounded health scares will encourage you to be more skeptical the next time you read about a new, supposedly dire, health "threat," and let's hope it will cause editors and journalists to more seriously consider whether a story really deserves coverage.

Elizabeth Whelan, Sc.D., M.P.H., is president of the American Council on Science and Health.