We all know to stay away from people with the flu, but should we also steer clear of sad people? It may seem unusual, but certain emotions and behaviors have the potential to be transmitted from person to person, especially people with an emotional connection. On the plus side, it seems laughter is not only the best medicine, but it is also contagious when you’re around it. Unfortunately so is loneliness, proving that misery loves company. You’d be surprised to learn what quirky traits you can pass on to your friends and family.

1. Loneliness

Ever feel like you’re alone while standing in the middle of a crowded room full of people you know? It’s not a cliché; loneliness can actually be passed between members of a social group. A research team led by University of Chicago psychologist John Cacioppo recruited 5,124 people involved with the Framingham Heart Study, a longitudinal study that began back in 1948. Each participant was asked to report on their emotions every two to four years. Researchers also collected the names of friends to construct an image of each individual’s social network. A pattern of loneliness that “infected” each person in the group eventually caused everyone to withdraw from the social circle. By the end of the assessment almost all members of the social group reported few friends they were close to.

"Loneliness can be contagious because lonely people not only tend to project their own feelings of loneliness and depression on to others, but with the rise of the internet and social media and the battle for attention competition, when a lonely person doesn't get heard, it just creates more loneliness and feelings of rejection," clinically trained marriage and family therapist, Stacy Lynn Harp, M.S. told Medical Daily.

2. Laughter

Much to the delight of comedians, being around someone who is laughing can cause you to breakout in laughter as well. When your brain hears the sound of laughter it forms a response that readies your face for the feeling of joy. Neuroscientists from the University College London who decided to test how infectious laughter can be hooked up volunteers to an fMRI to demonstrate the brain’s response to certain sounds. After hearing the sound of laughter, the premotor cortical region of the brain, area of the brain that controls our facial muscles, prepared their face to correspond with the sound it was hearing. Compared to negative sounds meant to provoke sadness and despondency, positive sounds that elicited joy and laughter were much more contagious with each participant.

“This response in the brain, automatically priming us to smile or laugh, provides a way of mirroring the behavior of others, something which helps us interact socially,” one of the study’s authors, Dr. Sophie Scott said in a statement.

3. Itching

After seeing someone around you scratch away a pestering itch, you may notice your own desire to start itching. Don’t worry, you didn’t catch some type of contagious skin disease. Similar to yawning, when you see someone itching, the same area of the brain that caused them to itch is also triggered in your brain. To put this theory to the test, British researchers asked 51 healthy adults to watch a series of videos that either showed a person scratching a part of their upper body or simply tapping that area of their body.  While watching the video, each participant was asked to report on whether they felt the urge to itch or not. Not only did most of the group verbally convey the urge to itch, 64 percent of the group actually began to itch after watching a video of someone doing so.

4. Stress

Unfortunately, sometimes stress is unavoidable. It can be communicated from person to person and even mother to child. A study conducted at the University of California San Francisco tested the emotional synchrony between 69 mother and their 12- to 14-month infants. After they were separated, mother and child were fitted with cardiovascular sensors and the mothers were exposed to either a positive signal including smiling, a negative signal such as frowning or no signal at all. Mothers who were exposed to negative signals were less likely to experience positive emotions and more likely to show signs of cardiac stress. When the mothers who were exposed to the negative signal were reunited with their child the infant’s heart rate quickly increased and mimicked their mother’s stressful response.

“When we are around stressed out or upset people we often feel their negativity or emotions in our own body,” award-winning author of The Alternative Medicine Cabinet, Kathy Gruver told Medical Daily. “We might not even be realizing that it's happening. Our brains can't tell the difference between what we are thinking and fantasizing about and what is really happening. So, if we are in the vicinity of someone who is stressed or sharing an emotionally charged story with us, we are going to, on some level, react with a stress response.”