In almost half of two-parent American families with kids, both parents work full-time. But when they come home from their paid labor, women are still doing more work (almost twice as much) when it comes to household chores. This trend was first discussed in the 1970s, when it was dubbed "the second shift.")

Part of the problem is that men think they're doing equal duty, as so many of them reported in a Pew Research Center poll of more than 1,800 American parents. Women in that same poll disagreed, saying they do more work, and according to several new studies, when couples are asked to keep a time diary (a more reliable way to get data than asking people what they remember doing), the diaries prove that women are right.

The data from the most recent study (April 2015), show that women spend almost twice as much time (18 hours to men's 10) doing the at-home grunt work like cleaning. Men not only do less, but they also choose the more enjoyable stuff like playing with kids or supervising bath time.

You'll notice that I specified parents in the graphs above. That's because researchers have found that this increased work kicks in when a baby arrives. Prior to that milestone, work is mostly evenly split between to partners if they both work full-time. And the situation isn't improving: While men are spending more time caring for kids than ever before, they're actually spending less time on housework than they did in the 1990s. Not surprisingly, women are doing more. And that time doing housework comes directly out of women's work and leisure time, according to the time-use surveys.

Why does it matter? Well, aside from issues of plain-old fairness, it's telling that over 40 percent of working mothers with partners told the Pew poll that they "always feel rushed," whatever they're doing. It's not a huge leap to assume that someone who feels that way is chronically stressed, which has both mental and physical health impacts. And women who feel burdened at home and stressed out are less likely to go after that promotion or take on additional tasks at work — tasks that are key to moving ahead.

And while some have argued that women biologically pay more attention to and are closer to their children — and therefore "naturally" spend more time caring for them — that same argument can't be made when it comes to mopping the bathroom floor or cleaning the fridge. As Bryce Covert writes in the Nation: "... there’s no biological determinant for housework. No gender is physically predisposed to want to do the dishes or take out the trash."

Covert digs into why this unfair situation exists, and her thinking goes back to childhood, where on average, girls do two hours more housework a week than boys and are less likely than boys to be paid to do that work. This is where the cleanliness of the home is first instilled as a girl's concern. So even if they're making the same salary as their husband when they're 35, women tend to feel that a messy home is their responsibility. Parents' examples matter too: Sons of working mothers spend more time sharing chores when they grow up and daughters of moms with jobs earn more money and are more likely to be bosses. Sons of stay-at-home moms do markedly less housework as adults. (Perhaps that explains the strange fact that men who are unemployed still do less housework than employed women.)

And when women do ask men to do their part? Well, they risk being classified as a nag. It's a no-win situation.

The good news is that there's less housework for everyone to do — according to the American Time Use survey, there's 23 percent less housework than 50 years ago. And men are doing more than they used to; guys have more than doubled the amount of work they do and tripled the amount of time they spend with their children.

And then there's "choreplay" — the amusing idea that men who do more housework are seen as sexier by their wives — and have more sex and more satisfying sex lives. If you'd heard that the opposite was the case, the update is that info was based on old data from the '80s and early '90s — so the details were taken from an older generation.

Of course, all this will be a moot point once the housecleaning robots finally make their appearance, but until then, grab a mop guys, and enjoy the satisfaction of a clean home. After all, there are real rewards for housework, and they're available to all.

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.