As important as positive emotions are for us as individuals, they may be even more important for our relationships. They help us forge strong connections with others by breaking down boundaries that separate us from each other. By broadening our attention in ways that help us see ourselves as less distinct from others, they allow us to create all kinds of relationships, including romantic ones. When we are in romantic relationships we desire to expand ourselves by including our partner or spouse within our self and we associate that expansion of our self with the other. This influential self-expansion model of love is based on the research of leading relationship scientist Arthur Aron, professor of psychology at Stony Brook University. Aron argues that self-expansion is a catalyst for positive emotions. He and his colleagues use pairs of overlapping circles to ask couples about their relationship quality. On one end of their scale, the pair of circles does not overlap at all, and at the other end, the circles overlap almost completely. The researchers have asked thousands of couples to pick which pair of circles best depicts how they feel about their relationship. The more overlap an individual feels with his or her partner, the better the relationship is likely to fare. This simple measure has been more effective than more complex surveys and interviews at predicting which couples will stay together and which will break up.

While self-expansion triggers positivity, Barbara Fredrickson, Kenan Distinguished Professor at the University of North Carolina at Chapel Hill and the leading researcher on positive emotions, finds it works the other way around, as well. In a variety of experiments, she has found that even lab-induced positive emotions can help people see more overlap between themselves and others. These emotions can help people feel closer and more connected to their loved ones. And the more you continually kindle positive feelings in your relationships, the more connected and happy you feel overall.

Another way positive emotions can enhance relationships is through contagion. Just as we can pass colds along to our partners through physical contagion, so we can pass along our feelings to our partners through emotional contagion. Ever notice how when you spend time with your partner, you often wind up feeling the emotions he or she is experiencing? Emotional contagion is rather complex and often happens below the level of our consciousness. It results from the fact that we are built to mimic each other. As infants, we start mimicking our parents soon after we are born, behavior that is critical for our development and constitutes a primary pathway to learning and growing throughout our lives. Emotional contagion results from our tendency to copy or synchronize our facial expressions, vocalizations, postures, and behaviors with those around us, and as a result take on their emotional landscape.

So although the underlying processes are different, we can talk about catching emotions from others, just as we can talk about catching their colds. And just as there are those who are more susceptible to catching colds from others, there are those who are more sensitive than others to their emotional environment, and thus more likely to pick up the emotions of those around them. This experience, of course, is even more common than the common cold. How many times have you found yourself in a situation in which you are doing fine, but then you spend some time with a partner who is not doing fine? Soon you begin picking up the other person’s negative emotions, and before you know it, you are not doing fine, either. Your partner’s negative emotions have spread to you, and you are now feeling them yourself.

Researchers have studied this phenomenon by various means and have documented ways in which emotional contagion can result in behavior change. One such researcher is Sigal Barsade, now professor of management at the Wharton School at the University of Pennsylvania. Her research indicates that negative emotions can not only spread to those around us but also negatively affect behavior and performance. Sigal’s study and others like it show us how important it is to be aware of our emotional states. The negative emotions we are feeling can easily spread to our partners and this can affect not just how we feel but also how we behave.

The good news is that we can catch positive emotions from others as well. They can buoy our spirits, fill us with gratitude, and energize us with interest. These states broaden our thinking and open our hearts, enabling us to connect more closely with others.