In the 14th century, bubonic plague instigated such widespread panic and terror that society broke down. Europeans attacked foreigners and non-Christians, blaming them for the epidemic. Fear of infection drove many to purchase expensive amulets and herbs in useless attempts to ward off the disease that was ravaging the continent. People locked themselves away to pray and punish themselves for days at a time, believing the disease was the wrath of God.

The fear was driven largely by a lack of knowledge — people didn’t know how the disease spread, where it came from, or how to control it. It’s easy to see why, without modern medicine, 14th-Century Europeans were consumed by fright at the thought of the Black Death and lashed out in response. Today, information about every health condition is only a mouse click away, but this armor of information may not always protect us well. The diseases we fear the most aren’t always those that we should, and it seems no amount of knowledge can change this.

The Ebola Problem

Though we’ve largely managed to quell the destruction caused by infectious diseases in the developed world, one made a particularly powerful resurgence in 2014. The Ebola virus, with all its ghastly, bloody symptoms, spread rapidly through West Africa to become the deadliest outbreak of the disease since its discovery. The condition was of little consequence to Americans and other Westerners until United States missionaries and doctors began contracting it in Africa then coming back for treatment.

When Emory University Hospital in Atlanta was treating one of these infected Americans, the Centers for Disease Control got a glimpse of the country’s concerns. Director Tom Frieden said the agency received nasty emails and more than 100 critical phone calls in which people asked why sick workers were being allowed back into the U.S. Health experts, however, never believed the public would be in danger.

“I don’t think it’s in the cards that we would have widespread Ebola,” Frieden told CBS News in 2014. He said the disease was spreading in hospitals in Africa because of poor infection control and burials where people touched the bodies of Ebola victims. That would never happen in the U.S., he said, because we “know how to stop it here.”

Frieden’s words, along with those of many other experts, were apparently of no value to American citizens. An October 2014 survey found that 27 percent of Americans viewed Ebola as a “major public health threat” — a figure that doubled in less than a month.

“Ebola is an agent that evokes a lot of fear and can result in societal disruption,” the Mayo Clinic’s Dr. Pritish Tosh told HealthDay. “There’s a reason why it’s considered a possible bioterrorism agent. So any time you have cases in the United States, there is a heightened amount of anxiety.”

Being frightened of Ebola as a disease makes sense. After all, it has a low survival rate and excruciating symptoms. But the study showed that Americans’ fear is clouding their reason.

“Three out of four polled said they are concerned that people carrying Ebola will infect others before showing symptoms themselves,” the paper read. This is medically impossible, though — Ebola is spread only from one symptomatic person to another. Poll respondents even said that they were going to cancel or cut back on holiday or business travel because of Ebola, even if they weren’t going anywhere that had seen the virus.

The public didn’t react to Ebola in the most logical manner, probably because it’s such a lethal, unfamiliar disease. When it comes to conditions that are very likely to affect us, however, we keep our heads a bit better.

Common Condition, Common Fear

In fact, sometimes we can be downright blasé about the biggest risks we face. “While public health priorities should focus on the largest or fastest-growing threats, fear is a personal thing that doesn’t always match up with objective numbers,” wrote Beth Skwarechi on the PLOS blog Public Health Perspectives. “Influenza kills more people each year than Ebola ever has, but that doesn’t automatically make it scarier.”

We may freak out over unusual diseases, but how do our fears match up to the leading causes of death? According to the Centers for Disease Control, the top five causes of death in America are as follows: heart disease (614,348 deaths annually), cancer (591,699), chronic lower respiratory diseases (147,101), accidents (136,053), stroke (133,103), and Alzheimer’s disease (93,541).

In a 2011 survey, the Metlife Foundation asked more than 1,000 U.S. adults which disease they feared the most. Forty-one percent of respondents reported that their biggest fear was cancer, followed closely by Alzheimer’s. Heart disease, stroke, and diabetes followed more distantly at 8 percent, 8 percent, and 6 percent, respectively.

The public’s fears matched up with true threats surprisingly well, but the researchers pointed out some nuances among the results. They note Alzheimer’s second place finish as a frightening disease may in part be due to lack of knowledge; just like the unknown contributed to panic during the Black Death, our lack of available information about Alzheimer’s leads to its scary status. Sixty-two percent of respondents admitted knowing nothing or very little about Alzheimer’s, and there isn’t a ton to know — the disease remains mysterious even to researchers.

The researchers also noted that, while heart disease is the top killer in America, only 8 percent of those surveyed said it was their top fear. Heart disease is not the deadliest disease by a hair, either — taken together, the fourth through 10th leading causes of death in 2010 still don’t equal the number of deaths heart disease causes. There are a multitude of risk factors that affect heart disease, including obesity, high cholesterol, high blood pressure, and poor diet — things many, and in some cases most, Americans struggle with. Though cancer is certainly a reasonable thing to fear, discounting heart disease’s lethality could be dangerous.

Americans in the 21st Century may not be panicking about any diseases on a daily basis, but that hardly means we have a good handle on what really has the potential to harm us. We fear Ebola, a comparatively distant threat, but brush off heart disease, something every one of us should be concerned about.