That perennial argument about who takes out the garbage does more than make you upset at your spouse; it can inhibit your immune system and interfere with healing. And if the relationship includes a lot of upsetting arguments, it can have even more powerful effects on the immune system.

That's the finding of a new study that tracked the chemicals involved in healing following both positive and negative interactions between married couples.

Scientists from Ohio State University's Institute for Behavioral Medicine Research recruited 42 couples, married an average of 12 years, and had them spend a night at a hospital. The couples were given tiny blisters on their arms using a suction technique and then, after a positive, supportive conversation, were monitored for the chemicals that regulate wound healing. Two months later, they returned for a second test, but this time they were told to discuss something that they disagreed about.

The study, published in the current Archives of General Psychiatry, found that the blister wounds took a day longer to heal following the upsetting discussion. The couples who were consistently more negative—more disgusted and more hostile, for example—took even longer to heal. They also showed high levels of other potentially damaging immune-system chemicals in their bloodstreams, suggesting that sustained hostility may increase the chances of developing chronic diseases—like cardiovascular disease, type 2 diabetes, and Alzheimer's disease—that involve inflammation.

"We knew that stress affected healing, but we didn't know it affected it so profoundly with such a minor event," says study author Janice Kiecolt-Glaser (whose collaborators included her husband, Ronald Glaser). The results point to the importance of reducing stress before surgery—and suggest that while marriage in general is associated with longer life spans, a marriage rife with conflict and stress may actually hurt you.

This is especially true for women, who have been shown to be more sensitive to hostility and disagreement in relationships.