As some parts of America gingerly begin to open up after months of near-total lockdown, people have questions. Will it be safe to take a train? A plane? Visit the hair salon? An indoor restaurant?

There are many knowable parameters in the equation: your health; the prevalence of cases where you live; the safety precautions being taken anyplace you want to visit. But the final answer may depend on your individual risk tolerance for exposure to infectious disease.

Most Americans alive today have never before had to make that self-assessment.

In the past, deadly outbreaks of plague, flu and polio were regular occurrences. Up until the mid- to late 20th century there were mumps, measles and chickenpox to contend with.

In a world of effective antibiotics and antivirals and other treatments, deaths or even serious illnesses from infectious disease seem nearly incomprehensible. So our fear is enormous, and our risk tolerance for exposure is just about zero.

I hear too many people saying “I’m not going back to life until there’s a vaccine” — as if that will immediately eliminate the risk. It won’t. Even if one of the current vaccine candidates works, it could be quite a while before it’s widely distributed. And to be approved by the Food and Drug Administration, it must protect only half of the people taking it from infection.

For the foreseeable future, we will be living in a world with some level of the coronavirus out there. So if we want to get out of our bunkers, we all need to take stock of our risk tolerance.

As a doctor, I worked in a New York City emergency room and in a remote coastal clinic in Kenya, and then I became a journalist covering disease. I’ve had to measure my risk tolerance for infection in different situations.

Once, collecting blood from an AIDs patient, I couldn’t feel the artery through my glove. The glove came off.

Treating a patient with multi-drug-resistant tuberculosis, I pulled my surgical mask a little tighter, made sure the windows were open and — irrationally — tried to breathe in less.

Reporting from the animal market where the SARS outbreak is thought to have started, I told myself that I should be OK, since it was outdoors. But I stayed away from animals being slaughtered, didn’t touch any surfaces and took off my shoes before entering my hotel room.

Note that these decisions do not mean ignoring the data and infectious disease specialists’ recommendations, as some conservatives are doing as they push ahead to reopen schools, businesses, restaurants and sports events.

Actually it’s kind of the opposite: Accepting risk doesn’t mean throwing caution to the wind. It means taking all precautions and deciding you can live with the very reduced risk that remains.

With the coronavirus, the only way to possibly eliminate risk is essentially to move to a house in the countryside and live in your family bubble. And many Americans, particularly wealthy ones, have done just that. This personal response was extreme, but it felt rational to many people because our national response to the coronavirus was so scattershot, flat-footed and incompetent.

But isolation is wearing thin.

So as states and cities engineer sensible reopening policies, everyone is going to have to assess their risk tolerance and cautiously push their personal boundaries bit by bit.

Some, of course, never got to make this decision. Risk tolerance is about duty and conscience but very often it’s also about how much you need a paycheck.

Doctors, nurses and others who work in health care had no choice but to dive in. These folks did not, as so many have claimed, go into the profession “knowing the risks.” They came to work knowing that the risk of infectious diseases could be controlled with careful precautions. That’s why they felt angry and betrayed when they were asked to fight the novel coronavirus without an adequate supply of protective gear or (in some places) training about the new pathogen. And, tragically, some died as a result.

Now many physicians I know in COVID-19 hot spots say they actually feel safest in the hospital, where procedures like masking and sanitizing are assiduously followed. (Hell hath no fury like a surgeon who witnesses a medical student touch a sterile surface with an unsterile hand.) In contrast, on the sidewalk, the coronavirus could be roaming free if people aren’t wearing masks.

Which is why masking should be mandated and enforced. It’s not just about your individual risk tolerance but about keeping everyone safe.

In addition to wearing masks and social distancing when not at home, we should avoid prolonged periods in indoor spaces with crowds or strangers; wash or sanitize our hands — a lot — and try not to touch “high-touch” surfaces that hundreds of people have grabbed before. (Note to my local post office: You should have some kind of automatic door rather than require everyone to pull the handle!)

And we have to demand that anywhere we go — bookstores, medical offices, trains or hair salons — requires that patrons follow these guidelines. I, for one, won’t enter if they don’t.

I do not blame teachers for being unwilling to return to school in places where administrators and officials have been in denial about COVID-19 or have been unwilling or unable to do this preparatory work. But once schools have put in place appropriate science-based steps, most teachers (those not in high-risk groups) should return to their jobs.

COVID-19 is a very serious disease. But it is not the Black Death, which killed up to half of Europe in the 14th century. A vaccine, when and if it arrives, will be a big help. But in the meantime, we have science. We know what causes COVID-19. We are learning more about how to detect, prevent and treat it every day.

So instead of taking your temperature and checking your pulse oximeter reading twice a day, it may be time to take stock of your risk tolerance. In those places where governments, businesses and administrators have set the stage properly, we can — with sensible precautions — begin to live again.