You can’t quite see the mental load the way you can see a pile of laundry or an armful of groceries, but that’s part of the problem. Underpinning every household is a wealth of activity and thought that runs just beneath the surface, keeping everything from breaking down into chaos. What’s in the fridge? Whose birthday is coming up next? How long have those dishes been there? The mental load is the endless to-do list of tasks and data that looms in the mind, a complex network of responsibilities that allows us to get anything done in the first place. In heterosexual relationships and family units, it generally falls to the woman.

Back in the 1990s, Dr. Susan Walzer, a professor of sociology at Skidmore College, identified what she termed “worry work.” She interviewed 25 hetero...