The same trend, however, was not reportedly found in relationships with children or friends.
Experts said told LiveScience that the results could be a consequence of accumulated contact with a spouse, such as nitpicking or frequent demands. Though they previously may have existed only as a minor annoyance, they are likely to develop into a major pain.
But accumulated irritation has its silver lining, according to the study.
"As we age and become closer and more comfortable with one another, it could be that we're more able to express ourselves to each other," lead study author Kira Birditt told LifeScience. "In other words, it's possible that negativity is a normal aspect of close relationships that include a great deal of daily contact."
While it could breed unhappy couples, experts say the increase in negativity could simply be a normal part of relationships.
"Because we found that pattern was overall among the participants, it appears to be normative," Birditt said. "It's not something unusual that happens."
Click here for more on the study.
