Though women had been leaving their homes to work in factories for decades, Kogan writes, the end of the 19th century saw a conflation of multiple social anxieties, from cholera panic left over from the Civil War to Victorian preoccupations with modesty and privacy, particularly concerning the body and bodily functions, to the mounting task of "protecting" fragile women in the public sphere. At the same time, burgeoning evolutionary biologists were peddling the theory that women were physically and mentally inferior to men. Thus, a collision of Victorian paternalism and junk science birthed the gender-segregated public restroom.

As women became more active in various aspects of public life, they had to be fitted into the interstitial spaces of a world that had not been built for them. (Male) architects and (male) city planners began to section off areas for them to exist out in the world, but without radically disrupting the precious social fabric of Man’s Land. These male decision-makers created separate spaces for women in everything from railroad cars to department stores to post offices. Public libraries, long since “bastions of male status that often excluded women,” began cordoning off women’s spaces as soon as they were provided any access (since some men were concerned that women would be “disruptive to the concentration of serious readers”). These spaces, decorated like living rooms and stocked with women’s magazines, provided discreet access to separate women’s restrooms, precursors to the fancy ladies’ rooms that can still be found today in high-end hotels and country clubs. Apparently, if a woman needed to venture into the messiness of a man’s world in the late 19th century, she had to be placed within a familiar pocket of domesticity.

More than that, however, her weaker body needed to be protected from the bathroom’s threat of dirt and disease. Kogan points out that many of the first laws mandating gender separation in water closets were actually “adopted by states as amendments to and extensions of earlier protective labor legislation aimed at women workers; these laws were not intended as neutral regulations for the mutual benefit of men and women alike.”

But of course, these comfortable, domestic, and hygienic safe havens were only ever afforded to white women. Decades before the “men in dresses will attack vulnerable ladies” ruse would be used to justify anti-trans bathroom discrimination, insinuations that racially desegregating public restrooms would harm white women proved a formidable barrier to achieving civil rights for black Americans. Today’s bugbear of the queer sexual deviant is directly preceded by the profoundly racist assumption, popularized after World War II, that black men would prey on white women should racial parity be established in public restrooms. As Gillian Frank detailed last November for Slate, the perceived sexual threat of sharing bathrooms with black people was coupled with a sanitary one — white women “emphasized that contact with black women in bathrooms would infect them with venereal diseases.” While separate women’s restrooms were indeed the product of sexist beliefs regarding women’s fragility and (lack of) power, white women were still afforded far more favorable restroom conditions than women of color — conditions they maintained for themselves through racist fearmongering.

By the 1990s, a full century after the first slew of gender segregation mandates, one would assume that the relics of Victorian paternalism would no longer apply to a modern world. The civil rights movement had already seen the abolishment of bathrooms segregated by race (which, while a clear step forward, by no means ended racial discrimination in public restrooms — trans people of color, for example, report problems using the bathroom at far higher rates than their white counterparts). But public restrooms remained steadfastly segregated by gender, and even the country’s most powerful women were still battling for equal access to physical slices of public life.

As recently as 1992, female U.S. senators did not have their own restroom. Before Senate Majority Leader George Mitchell announced that a new bathroom for women would be built on the Senate floor, there was only a men’s room there, reading “Senators Only” (which assumed, of course, that senators could only ever be — and would only ever be — men). The female senators were forced to walk a long way from the floor to relieve themselves among the tourists. And even when a restroom for female senators was finally completed in 1993, it had only two stalls; 20 years later, by which time there were 20 women in the Senate, long lines were a daily nuisance. In 2013, when a few of the senators spoke up about the inconvenience, two additional stalls were added to their restroom. Meanwhile, in the House, congresswomen also had to schlep to the tourist bathrooms in Statuary Hall until the 76 female members of the House finally got their own restroom in 2011.