Couples who are best friends and split the chores and childcare have less sex, says Lori Gottlieb, psychotherapist from Los Angeles.

According to her article, which appeared in The Guardian, 64% of couples with children under 18, both husband and wife work. “There's more gender-fluidity when it comes to who brings in the money, who does the laundry and dishes, who drives the car and plaits the kids' hair, even who owns the home,” she writes. But the problem is – “the very qualities that lead to greater emotional satisfaction in such marriages may be having an unexpectedly negative impact on these couples' sex lives.”

A recent study that appeared in American Sociological Review last year surprised many, since it showed that though marriages improve by becoming more equal, the amount of sex in these marriages does not improve, too. “Specifically, if men did all of what the researchers characterised as feminine chores such as folding laundry, cooking or vacuuming – the kinds of things many women say they want their husbands to do – then couples had sex 1.5 fewer times a month than those with husbands who did what were considered masculine chores, such as taking out the trash or fixing the car.”

Some might view a study like this with skepticism, Gottlieb says, yet she insists that as a psychotherapist who works with couples, she has noticed a curious thing: “being stuck with all the chores rarely tends to make wives desire their husbands. Yet having their partner, say, load the dishwasher doesn't seem to have much of an effect on their libido, either.” Many of Gottlieb’s colleagues have observed the same thing.

It’s interesting that in the happiest couples, husbands do help their wives with housework. “Couples in which the husband did plenty of traditionally male chores reported a 17.5% higher frequency of sexual intercourse than those in which the husband did none.”

Besides, Lynn Prince Cooke, professor of social policy at the University of Bath, says that the couples who share breadwinning and household duties are rather happy overall and are less likely to divorce.