An unhappy relationship can hurt far beyond the emotional strain of love unraveling. Vicious arguments are associated with poor sleep, heart pain and muscle pain, while family members, including children, may become more vulnerable to physical and mental health problems.

Happy relationships, by contrast, can support health and longevity. Poor quality close relationships are considered a health risk factor equal to or greater than smoking or insufficient exercise, and their effects may raise the risk of an earlier death by gradually damaging health.

Research nevertheless offers hope for couples committed to changing their relationship. One important finding is that the subjects couples argue about often remain remarkably consistent, even when the relationship lasts for years.

These recurring disputes are known as perpetual or gridlocked issues. Carrie Cole, a psychologist and director of research at The Gottman Institute for couples therapy in Seattle, says they may involve finances, parenting, sex, power or apparently smaller concerns such as neatness.

In one study, psychologist John Gottman and his team observed couples during disagreements and assessed them again four years later. They found that 69% of the time, couples were still arguing about the same types of issues they had debated four years earlier.

Money produces some of the most persistent and heated conflicts, while an unequal division of housework can increase tension and the likelihood of divorce. Yet disagreement itself is not necessarily alarming because both happy and unhappy couples argue.

The more revealing difference is how partners treat one another during conflicts and outside them. Cole identifies criticism, contempt, defensiveness and stonewalling, meaning withdrawal and refusal to engage, as behaviors that can signal a relationship moving toward separation.

“Those four behaviours will kill a relationship,” Cole says. Yet she also offers a crucial qualification: “they are fixable, if the couple wants to fix them.”

Persistent criticism from a partner has also been found to significantly predict an earlier death. Arguments marked by criticism, aggression and hostility are considered destructive and may ultimately increase the risk of divorce, while respectful, curious and kind discussions can strengthen a relationship.

Responsiveness is another important factor. Feeling that a partner listens, understands and provides support is associated with greater marital satisfaction, and research indicates that such responsiveness may buffer inflammation while supporting physical health and longevity.

Kindness and cooperation can build goodwill over time. One study that followed married couples for 20 years associated shared decision making and an equal division of housework with greater marital happiness and lower conflict.

The quality of conflict may even shape sleep, with destructive arguments associated with poor sleep and constructive arguments associated with better rest. Changing bitter patterns can feel nearly impossible, but a substantial body of evidence indicates that couples can improve, including with therapy.

Research suggests couples therapy has a positive impact on 70% of couples who participate. It can improve relationship problems, satisfaction and emotional intimacy, prevent relationship distress, and help with individual emotional or physical health concerns.

Jay Lebow, a couples therapist and clinical professor of psychology at the Family Institute at Northwestern University in Evanston, Illinois, says empathy is often badly diminished by the time couples seek help. “How do we rebuild our empathy?” is one of the central challenges, he says.

Progress can appear through better speaking and listening, as well as an ability to step back and examine what is happening between partners rather than focusing only on perceived faults. Cole sees hope when one partner says, “I can see why you would feel that way.”

That response signals an ability to accept the other person’s perspective as valid, even when the partners disagree. Curiosity is another promising sign, particularly when someone asks, “Tell me more about that, how did you come to believe that?”

Cole describes a couple whose repeated disputes about money were rooted in their different responses to growing up in poverty. The wife sought security through saving and careful budgeting, while the husband wanted to enjoy his earnings, buy nice things and feel included in society.

Therapy helped them listen to each other’s painful experiences and understand the goals those experiences had shaped. They reached a compromise about how much money to save and how much each could spend freely.

Motivation matters greatly, Lebow says, because even an excellent therapist may struggle to help clients who do not want to change. Highly motivated couples, however, may still make progress even when the therapist is less effective.

Therapy may also help couples who decide to separate by reducing hostility and helping them manage the possible mental health effects on themselves and their children. Lebow says listening and empathy can benefit distressed couples, separating couples and even people whose relationships are already good.