Covid-19, the invisible enemy now bearing down on 328.2 million Americans, is tailor-made to induce fear and anxiety, prompting both rational and irrational behavior and, if the emotional stress persists, perhaps causing long-lasting harm to health.

We’re staring down an alien virus our bodies have never before encountered and which we are currently unable to control. There is no vaccine yet available to prevent Covid-19 or drug proven effective to fight the illness, limiting our ability to protect ourselves. So we buy reams and reams of toilet paper because it’s something we can do to give us a feeling of dominance over a force that threatens to overwhelm us.

“There’s never been a time in modern human history when every person is seriously worried about the same thing at the same time,” said David Ropeik, a consultant on risk management and former instructor in risk communication at the Harvard School of Public Health. And there’s never before been a ubiquitous threat that can be so instantly broadcast to a world of 7.8 billion people.

“We’re being inundated with a constant flow of scary information that overwhelms our ability to be dispassionate,” said Mr. Ropeik, author of “How Risky Is It, Really? Why Our Fears Don’t Always Match the Facts.” “Our brains are screaming to give the coronavirus more weight, challenging our ability to recognize that most people are actually at low risk.”

As with other calamities, it’s the bad news that gets the most attention, not the apparent fact that most people who become infected develop no symptoms or only mild ones and recover fully within a week or so.

Compounding a sense of doom for some people is their inability to evaluate risk and the fact that what is an acceptable risk for one person is intolerable to another. Following the terrorist attacks on Sept. 11, 2001, many people were afraid to fly and instead drove thousands of miles, incurring a far greater risk to life and limb yet instilling a feeling of control with their hands on the wheel and foot on the gas.

“A risk we choose seems less dangerous than a risk that is imposed on us,” Mr. Ropeik observed.

Not that it’s inappropriate to feel anxious about the risk we all now face, especially if that distress reminds us to be diligent about social distancing, avoid physical contact with people who do not share our household, wash our hands often and well and keep them off our faces and out of our eyes.

But while a certain amount of worrying can help motivate you to protect against possible exposure to the virus, compulsively reading or tuning in to the bad news about Covid-19 throughout the day is unlikely to enhance your emotional or physical well-being.

There are important health reasons to tamp down excessive anxiety that can accompany this viral threat. We have a built-in physiological response to imminent danger called fight-or-flight. Hearts beat faster, blood pressure rises and breathing rate increases to help us escape the man-eating lion.

Underlying these stress-induced changes are hormones like adrenaline, noradrenaline and cortisol that can cause trouble if they persist too long in our circulation. Sustained anxiety increases the risk of cardiovascular disease, digestive problems, clinical depression and, ironically, infectious diseases like Covid-19 by weakening the immune response to a viral infection.

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“The stress of Covid-19 is now acute, but if it persists long after April, which it likely will, it will take an enormous toll on world health,” Mr. Ropeik said.

Thus, in addition to heeding the recommended personal precautions to avoid an infection, people feeling unduly stressed about the pandemic might try to minimize the damage caused by unmitigated anxiety.

A psychotherapist I know has advised his patients to limit their exposure to the news and discussions about Covid-19 to one hour a day and, if possible, in only one location, then use the rest of the day and other parts of the home for productive or pleasurable activities.

You can bolster positive feelings by doing something good — for your neighbors, the essential workers in your community, or strangers now lacking adequate resources to care for themselves or their families. I’ve gone through closets and bagged tons of clothing to give to those in need, and I’ve contributed to a GoFundMe site that is raising money to provide meals for workers at the neighborhood hospital, which also helps support local restaurants now limited to takeout only. There are similar donation sites now throughout the world.

You can also tackle long-neglected chores in and around home. Some ideas: Clean out the refrigerator or pantry, take the stove apart and wash everything down, repair torn clothing (including socks!), go through bookshelves and pack up books not worth keeping that you read long ago or that are now out of date.

And pay attention to leaders like New York’s Governor Andrew M. Cuomo, who has emphasized that the most critical step in countering the damage wrought by this novel virus is to flatten the curve of rising infections, both to keep from overwhelming our health care systems and to buy time to develop more effective strategies and, hopefully, therapies.

Few people, it seems, understand exponential growth well enough to appreciate the devastation that can result from the current rate of infection. In any new location, the infection may smolder for a brief period and then suddenly explode and take everyone by surprise, said Paul Slovic, a professor of psychology at the University of Oregon and president of Decision Research, a group of scientists who study decision-making and risk. “Then you regret not having acted sooner to contain the threat,” he said.

Dr. Slovic, author of “The Perception of Risk,” explained exponential growth in an article he and Howard C. Kunreuther of the Wharton Risk Management and Decision Processes Center wrote in Politico last month: If a single lily pad in a pond doubled each day, after 40 days only 1/256th of the pond would be covered, but by day 47 half the pond would be covered and one day later, lily pads would cover the entire pond.

The failure to recognize the potential for an exponential increase in Covid-19 when it began in China resulted in a squandered opportunity to control its spread. In just 67 days there were 100,000 cases worldwide; 11 days later another 100,000 cases, and four days after that, yet another 100,000 cases.

Drs. Slovic and Kunreuther likened the trajectory of Covid-19 to climate change, which has been gradually worsening for many decades. As with the virus, our failure to act early on has not flattened the curve and is likely to result in an explosive surge that will devastate huge populations, with no vaccine or drug able to alleviate the damage.

Jane Brody is the Personal Health columnist, a position she has held since 1976. She has written more than a dozen books including the best sellers “Jane Brody’s Nutrition Book” and “Jane Brody’s Good Food Book.”

A version of this article appears in print on , Section D, Page 9 of the New York edition with the headline: Fear of the Virus Can Be Just as Dangerous. Order Reprints | Today’s Paper | Subscribe

  • Updated April 11, 2020

    • When will this end?

      This is a difficult question, because a lot depends on how well the virus is contained. A better question might be: “How will we know when to reopen the country?” In an American Enterprise Institute report, Scott Gottlieb, Caitlin Rivers, Mark B. McClellan, Lauren Silvis and Crystal Watson staked out four goal posts for recovery: Hospitals in the state must be able to safely treat all patients requiring hospitalization, without resorting to crisis standards of care; the state needs to be able to at least test everyone who has symptoms; the state is able to conduct monitoring of confirmed cases and contacts; and there must be a sustained reduction in cases for at least 14 days.

    • What should I do if I feel sick?

      If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.

    • Should I wear a mask?

      The C.D.C. has recommended that all Americans wear cloth masks if they go out in public. This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms. Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing. Part of the reason was to preserve medical-grade masks for health care workers who desperately need them at a time when they are in continuously short supply. Masks don’t replace hand washing and social distancing.

    • How does coronavirus spread?

      It seems to spread very easily from person to person, especially in homes, hospitals and other confined spaces. The pathogen can be carried on tiny respiratory droplets that fall as they are coughed or sneezed out. It may also be transmitted when we touch a contaminated surface and then touch our face.

    • Is there a vaccine yet?

      No. Clinical trials are underway in the United States, China and Europe. But American officials and pharmaceutical executives have said that a vaccine remains at least 12 to 18 months away.

    • What makes this outbreak so different?

      Unlike the flu, there is no known treatment or vaccine, and little is known about this particular virus so far. It seems to be more lethal than the flu, but the numbers are still uncertain. And it hits the elderly and those with underlying conditions — not just those with respiratory diseases — particularly hard.

    • What if somebody in my family gets sick?

      If the family member doesn’t need hospitalization and can be cared for at home, you should help him or her with basic needs and monitor the symptoms, while also keeping as much distance as possible, according to guidelines issued by the C.D.C. If there’s space, the sick family member should stay in a separate room and use a separate bathroom. If masks are available, both the sick person and the caregiver should wear them when the caregiver enters the room. Make sure not to share any dishes or other household items and to regularly clean surfaces like counters, doorknobs, toilets and tables. Don’t forget to wash your hands frequently.

    • Should I stock up on groceries?

      Plan two weeks of meals if possible. But people should not hoard food or supplies. Despite the empty shelves, the supply chain remains strong. And remember to wipe the handle of the grocery cart with a disinfecting wipe and wash your hands as soon as you get home.

    • Should I pull my money from the markets?

      That’s not a good idea. Even if you’re retired, having a balanced portfolio of stocks and bonds so that your money keeps up with inflation, or even grows, makes sense. But retirees may want to think about having enough cash set aside for a year’s worth of living expenses and big payments needed over the next five years.