American husbands don't mind their wives making money—but over 40% of their combined income? Then it's time for the man cave. So says a new study that measured male stress in roughly 6,000 US couples over a 15-year stretch, CBS News reports. Husbands in the study said they were least stressed when wives earned roughly 40% of their combined income, but anything more became stressful. Male stress was measured in terms of feeling worthless, hopeless, restless, nervous, sad, or everything seeming like an effort. "These findings suggest that social norms about male breadwinning—and traditional conventions about men earning more than their wives—can be dangerous for men's health," says study author Joanna Syrda.
But there's nuance. Men who married women who already made more than them didn't seem bothered by it, the study says. And husbands who were the household's sole breadwinner also suffered from higher stress. How men and women perceived the value of earning also stood out: While 70% of men and women agreed that men need to be providers, 25% of men and 40% of women said women also need to provide. This as roughly a third of US women earn the same as their husbands, up from 12% in 1980, per Pew Research. "Women have been making relatively more and more money," says Syrda. "The trends are going one way. And it's interesting that the male breadwinner norm is so durable." (Read more household income stories.)