Whether it’s through shared meals, exercise routines, or even stress management strategies, partners tend to mirror each other’s behaviors.Over time, this creates biological similarities that go beyond genetics. These researches encourage us to think about how the choices we make with a partner can have long-term effects on our well-being.

We’ve all heard the saying, “opposites attract.” Maybe you know a couple where one person is outgoing and the other prefers quiet time, where one loves sports and the other can’t stand them, and yet, somehow, they make it work. At first glance, these differences make relationships exciting. And honestly, it’s comforting to believe that opposites attract, not to mention these mismatched pairs have long fed the belief that opposites attract. But recent research challenges this idea, suggesting that partners in long-term relationships are more similar than we think.

Recent research published in Nature Human Behavior reveals that people in long-term relationships share more similarities than differences—up to 89% of the traits examined by researchers. These similarities go beyond surface-level preferences like favorite foods or TV shows. Couples align on values, emotional tendencies, intelligence, political views, and even the age they became sexually active. As the years go by, this connection seeps into something even deeper: their biology.

Why do couples sometimes seem to share not just a home, but also health conditions? 

When two people share their lives, they inevitably influence each other’s health, sometimes for better or worse.

The phenomenon of couple concordance is explained through two primary perspectives. The first is the concept of assortative mating, which means people tend to form relationships with those who look like them or share similar traits. People are naturally drawn to partners with similar ethnic backgrounds, education levels, or physical attributes. In these cases, any genetic similarities between them might be due to their choice of partner rather than anything that develops over time.

The second perspective goes deeper and focuses on how being in a long-term relationship can shape health outcomes. A study in Atherosclerosis explored this idea by looking at couples from Japan and the Netherlands who did not share genetic links. Instead, their health began to resemble each other’s through shared lifestyle habits. Over time, the choices couples made—what they ate, how active they were, or how they managed stress—brought their health into alignment.

Emotional alignment in couples isn’t a new concept. Research has long suggested that people in long-term relationships tend to develop similar emotional patterns over time. A research examined couples who had been together for less than 15 years and those who had been married for more than 5 decades. Among the longer-term couples, researchers noticed a remarkable resemblance in their emotional responses to stress and happiness. These similarities seemed to have developed gradually through shared experiences and mutual influence.

Couples are constantly responding to the same environment and making sense of it together—the study referenced earlier research from 2011, which found that couples who had been together for many years showed a surprising synchronization in their emotional habits. Whether it was their coping mechanisms for anxiety or the way they celebrated successes, their emotional reactions closely mirrored one another’s.

Daily decisions—like how partners deal with conflicts, enjoy downtime, or handle stressful moments—play a key role. Over time, these choices shape not only how couples relate to each other but also how they navigate life’s emotional highs and lows together. 

The influence of long-term relationships on emotional well-being is not always smooth. For couples in strained or toxic relationships, the impact can be draining. Symptoms of anxiety and depression reportedly often develop in sync between partners. If one partner’s mental health declines, the other may also experience emotional exhaustion or burnout. This is understandable—when one partner withdraws or struggles emotionally, the other may begin to mirror that behavior, creating a cycle of emotional fatigue.

For couples in fulfilling relationships, though, this connection can be a positive force. Another study found that when at least one partner maintains a positive mindset, both are less likely to develop emotional distress, even under stressful circumstances. Emotional stability in one person appears to act as a buffer, protecting the mental health of both partners over time.

Long-term relationships can also provide valuable insights into emotional health. If one partner shows signs of chronic stress or burnout, it may hint at emotional patterns that both partners share. These patterns, if recognized early, can encourage couples to seek support before issues escalate. In good times and bad, understanding these shared emotional rhythms can lead to early interventions that promote well-being for both partners.