Think of something that scares you. Your heart starts to pound, you break into a sweat, your muscles start to tense. This classic fear response is important so that you can take action – “fight or flight” – and it can help protect you in a life-threatening situation.

It might also be contagious. You might think of fear as a personal emotion, but scientists have discovered that your fear can affect those around you.

This effect is clearest in animals. Animals have special chemicals called pheromones that they secrete in bodily fluids, and these chemicals are a way of communicating with other members of the same species. Pheromones can communicate many different messages, and fear is a common one. Imagine a bee that encounters a threat: It releases an alarm pheromone, which helps alert its colony to impending danger. The fear spreads, triggering a fight or flight response, and the bees are able to protect themselves as a group.

Humans also release chemical signals when they’re scared. When others smell these signals, research suggests they might also sense and experience heightened feeling. In one small study, researchers collected sweat from under people’s armpits after they had run on a treadmill and after they went skydiving. They made other people sniff both types of sweat to see their reaction. The scientists found that those who sniffed the skydiving sweat had more activity in the part of the brain called the amygdala, which is responsible for emotion processing.

Smell isn’t the only way that fear can be transmitted. As social beings, humans tend to mimic others. You’re more likely to smile if you see someone else smiling, and seeing someone else cry might also trigger your own tears to fall. That phenomenon is called emotional contagion, where a feeling (positive or negative) spreads between two people or throughout a group of people. Some emotions appear to spread faster and more effectively, though. High-arousal emotions like awe, anger, and anxiety or fear may be more likely to spread.

Many modern triggers that set off our stress response (such as work, dating, or the news) aren’t imminent dangers, and following the feelings of others may not help us. So can we resist emotional contagion? Researcher Sigal Barsade, who has studied emotional contagion for two decades, suggests creating a distraction from the source of contagion, projecting your own positivity, and speaking up if others are projecting negative emotions without realizing it. You don’t want somebody to bring down the vibe of a conversation if it means you’ll be brought down, too.