If you’ve ever had the misfortune of working with a toxic colleague or working for a toxic boss, you know how high the personal and professional cost can be. “Toxic” is a word that gets thrown around a lot these days, and there are endless guides on how to identify a toxic employee—and even how to categorize different types. (Apparently there’s a lot of bad behavior going on at work.) But I think we all know a toxic colleague when we encounter one.

These aren’t just difficult people, but as a seminal Harvard Business School (HBS) study on toxic workers put it, they are people who engage “in behavior that is harmful to an organization, including either its property or people.” In their most extreme form, the authors note, toxic workers can cost organizations billions of dollars, or even mortally harm current or past employees. But even “relatively modest levels of toxic behavior,” they write, “can cause major organizational cost, including customer loss, loss of employee morale, increased turnover, and loss of legitimacy among important external stakeholders.”

Not surprisingly, there is a strong connection between toxic workers and burnout. And I’m not talking about the toxic employee burning out! No, the people who are more vulnerable to burnout are the coworkers of toxic employees.

The McKinsey Health Institute conducted a study on toxic workplace conditions and burnout, using data from nearly 15,000 employees and 1,000 HR decision-makers in 15 countries. They found that toxic workplace behavior was the single biggest driver of employee negative outcomes, including burnout and intent to leave. Employees experiencing high levels of toxic behavior at work were eight times more likely to experience burnout symptoms such as exhaustion, reduced ability to regulate emotional and cognitive processes, and lack of engagement; and burned-out employees were six times more likely to quit within 3 to 6 months.

Why do toxic workers pose such a threat to their colleagues’ well-being and their risk of burnout? On one hand, the answer is simple: They make work life miserable. Who wouldn’t dread work or want to quit when a coworker or boss is disrespectful, demeaning, unfair, unethical, bullying, or engages in harassment? The more contact you have with such people, the higher your likelihood of psychological harm and of burning out.

There’s another, subtler thing happening as well. Toxic workers spread their negative emotions and harmful behavior to others. According to the authors of the HBS study, that’s the key difference between workers who are just difficult to deal with and workers who are genuinely toxic—their harmful behavior proliferates throughout the work environment, taking down multiple people or, potentially, even organizations. In fact, the authors found that exposure to toxic workers increases the likelihood of becoming a toxic worker yourself.

This happens in part because people automatically tend to mimic the emotions—and resulting behaviors—of the people in their environment. I’m sure we’ve all had experiences where we’re having a perfectly fine day until a stressed-out and anxious coworker comes in and unloads on us, leaving us feeling stressed out and anxious, or when a disgruntled colleague frequently vents about the latest thing that’s gone wrong, leaving us feeling drained and more pessimistic. Fortunately, though, it works both ways: Another person’s cheerful, upbeat mood is just as “shareable.” Whether it’s positive or negative, emotion can transfer from person to person, and it has the potential to drastically change your mood, outlook, and behavior.

The term for this phenomenon is emotional contagion. Just like the flu, emotions and emotion-based behaviors can spread from person to person, and it all happens in milliseconds, usually without our conscious awareness. A special part of our brain called the limbic system is wired to pick up on the emotional states of others, which are communicated verbally and nonverbally through body language, facial expression, tone of voice, gesture, and their general “vibe.”

At work, emotional contagion can play a powerful role in employees’ mood, outlook, productivity, sense of belonging, and overall performance. The effect is even more pronounced when it comes to a leader’s emotions. Studies in social psychology have shown that emotions are especially contagious in relationships where there is an inequality of power, such as between managers and employees. In addition to the regular, unconscious mimicry that happens between people, employees are more likely to actively try and align their reactions, moods, and emotions to that of their manager—and that happens if the manager’s mood is positive or negative, helpful or harmful. A recent study out of Denmark found that not only do managers transmit their stress to employees, the stress contagion effect lasts up to a full year.

Does this effect occur when it comes to burnout? You bet it does! Just as toxic behavior can beget toxic behavior, burnout begets burnout.

Researchers have found that the “burnout contagion effect” can occur between a single employee and another, or it can take root more rapidly, through group transmission. A burned-out employee’s negativity, diminished productivity, and lower well-being sets a negative example and influences how others feel and think. And, because burned-out employees tend to be low-performing, others may have to pick up the slack for them, and end up developing burnout on their own. Group transmission, on the other hand, usually occurs after some sort of big event that affects an entire team or organization. Layoffs, budget cuts, a new manager, or an acquisition that brings a new culture are all examples of big events that can inspire collective fear, confusion, or anger. If difficult feelings like these aren’t addressed by the organization, they can fester, and down the line, spark burnout among workers who interact with each other frequently.

Right now, let’s take a moment to assess your work environment. What words would you use to describe the emotional state of your workplace? What’s the general mood and tone? Do employees look and sound happy to be there? Is the vibe generally upbeat and optimistic, or does it feel tense, low-energy, or overwhelming? When things get tough, do people rally and support each other? Succumb to anxiety? Throw up their hands?

Whatever the emotional climate of your workplace, and whatever the employees’ collective emotional response to stress, remember that no one is an island. Emotional contagion is very real, and very powerful. Working with people who are constantly caught in the grip of negative emotion—and/or who do not respond to stress in healthy, productive ways—is a big red flag. Be aware that you’re in a high-risk environment and should take steps to protect yourself from the negative effects of emotional contagion well before it can develop into burnout.