Several days after the first mad cow was found in America, when the fresh news was gone and the follow-up stories started, the Wall Street Journal carried an article headlined SCIENTIFIC DATA OFFER NO PROOF OF BEEF SAFETY. An important story, since most of what we eat from cows is the meat, not the brain and spinal cord, which are the known risk materials from mad cows. Reporter Antonio Regalado spent the first 17 paragraphs of his story reporting about hints that meat from mad cows might be a risk for humans. Not until the 18th paragraph did he reveal that years of studies, hundreds of them at the height of the mad cow epidemic in the UK, had overwhelmingly proved that the meat from animals with mad cow disease poses no risk.

It was a classic example of how the news media handle health stories. The threatening or frightening stories get more coverage. The threatening or frightening aspects of stories get more emphasis within each report. Small wonder, really. Since these are essentially stories about survival, and survival is pretty high on the human list of priorities, news about anything that threatens our chances of getting to tomorrow is going to grab our attention.

In short, stories about health risks sell. Newspaper editors and broadcast news directors want stories the public will notice, stories that sell papers and boost ratings. And reporters—who aren’t concerned with corporate profits but are interested in their work getting the widest possible audience—highlight the aspects of their stories that seem particularly frightening. So health coverage tends to dramatize the risks of our behaviors, of what we eat and drink, of the things we’re exposed to in the environment. As a result, we the public are left poorly informed about what is more dangerous and what is less, and poorly informed about what we can and should do to improve our health.

It’s not a conscious process, this translation of every health report into a scare story. There’s something instinctual about it, which is well explained by a field of psychology known as risk perception. Research into the way humans subconsciously decide what to be afraid of and how afraid to be, by Paul Slovic of the University of Oregon, Baruch Fischoff of Carnegie Mellon University, and many others, has shown that certain characteristics tend to make us more or less afraid of risks.

And every characteristic that makes people more afraid makes a journalist more excited. I know from personal experience. I was a journalist for 22 years. I saw the adrenaline rush that comes from a dramatic story firsthand, in nearly all of my TV and print colleagues, and certainly fell victim to it myself far too often. Mea culpa.

The more threatening stories get more coverage.

Here is a short list of fear factors:

Trust. The less we trust the people who are supposed to protect us, or the people telling us about a risk, or the people or companies who make the product or service that creates the risk, the more afraid we are; the more we trust them, the less afraid.

Control. If we control our own fate, we are less afraid than if we don’t. When driving (even in Boston!), having the wheel in our hands produces a sense of control that causes us to downplay the risk of a crash, even though motor vehicle accidents kill more than 40,000 Americans a year.

Dread. Would you rather die by shark attack or by a heart attack in your sleep? The more awful death evokes more fear. That helps explain why many people fear cancer more than heart disease, even though heart disease kills roughly 160,000 Americans each year, or 26 percent more than cancer does.

Risk versus benefit. Imagine you are a paramedic or a nurse asked to take a smallpox vaccination. There is a one-in-a-million chance of death from the shot, and the disease, while life-threatening to anyone who contracts it, just isn’t around. Although the Bush administration raised the specter of smallpox as a weapon of terrorism, most “first responder” health care professionals said no to the risk, while low, of a vaccine that offered zero benefit. But imagine what would happen if there were a single confirmed case of smallpox in a Boston hospital. We’d all be lining up for the shot.

Children. Any risk to kids is scarier than the same risk to adults. How many news stories are there about abduction of adults?

Catastrophic versus chronic. A risk that kills a lot of people all at once in one place, like a plane crash or a terrorist attack, evokes more fear than another risk that kills the same number of people, but over time and space. For example: 2,899 Americans died on the fateful day of September 11, 2001. But 2,200 Americans die of heart disease every day. Who’s going to war over them?

There are other risk perception factors: We’re more afraid when things are uncertain, less afraid of risks we take by choice (talking on a cell phone while driving), more afraid of new risks (West Nile virus then) than ones we’ve lived with for a while (West Nile virus now), and more afraid of any risk we’re more aware of, either from news reports or from friends or family.

These factors affect journalists’ decisions about which health-related stories to cover and how to cover them. Journalists—reporters, editors, and news directors—are people, too. They intuitively sense which health news is freighted with the factors that will make people pay attention—and they play those factors up. So a product that is a risk to kids, that might kill them in some dreadful way, which is produced by an industry we don’t trust, is sure to get media attention.

Consider Alar, the chemical sprayed on apples to help them stay on trees a bit longer so they can ripen more. The risk it poses is tiny, with the chance of any kind of harm probably well below one in a million. But Alar is a product of the chemical industry (low trust); it is associated with cancer (high dread); and it affects products we feed to our kids. Alar got extensive and alarmist media coverage in 1989, and I was one of the reporters sounding the false alarm.

In contrast, a risk that is chronic, that we make worse by our own choices, and that leads to a relatively benign way of dying won’t get the headlines. The best example, again, is heart disease, the leading cause of death in America, which is rarely covered as dramatically as Alar was.

In short, the psychological factors of risk perception seduce the news media to over-dramatize certain hazards while playing down other dangers that may be more of a threat.

And that’s dangerous for public health. The media emphasis on perils that push our fear buttons causes us to worry about some things more than we need to, like pesticides on our food, and less about some things we should worry about more, like food poisoning. This can lead to dangerous behaviors by individuals (buying guns when crime is in the news, taking antibiotics we don’t need because of reports about anthrax). And constantly hearing about these exaggerated dangers takes a health toll. An endless drumbeat of alarms can raise our underlying level of stress, and stress is associated with a weakened immune system, heart problems, gastrointestinal problems, decreased fertility, decreased ability to form long-term memory, osteoporosis, and development of Type 2 diabetes.

This alarmism distorts the public health agenda as well. As citizens, we demand more government protection from the higher-profile risks, even though they may not be the greatest threats. These priorities can be seen in the federal budget. Remember that heart disease kills 26 percent more Americans than cancer does. Yet the National Cancer Institute has an annual budget of $4.2 billion; the National Heart, Lung, and Blood Institute has an annual budget of $1.8 billion.

By the standards of journalism as I learned them, it is not the news media’s responsibility to consider the effects of their coverage. It is their responsibility to report the truth, as best they can. But the truth is more than just getting the facts right, story by story. It’s seeing the bigger picture of which health stories really matter, and reporting on them accordingly. It’s being fair with the facts, so that information doesn’t automatically get more play just because it’s more frightening.

Television anchor Walter Cronkite used to sign off by saying, “And that’s the way it is….” Indeed, all that most of us know about the way it is in the world beyond our own personal experience is what the news media tell us, filtered through our own knowledge and biases. A skewed sense of health risk is going to alter the way we live our lives and the pressures we put on health policy-makers to protect us from some risks more than others. Editors and reporters should provide health news that has both drama and balance. There is room, and a public need, for both.

David Ropeik is director of risk communication at the Harvard Center for Risk Analysis and a former reporter for WCVB-TV and science columnist for The Boston Globe.