Caitlin Flanagan is a contributing editor at the Atlantic and the author of “Girl Land.”

Caitlin Flanagan is a contributing editor at the Atlantic and the author of “Girl Land.”

Oh, did Constant Reader heave a big sigh when she saw the title of this new book: “Unmentionable: The Victorian Lady’s Guide to Sex, Marriage and Manners.” She expected another “I. Have. No. Words.” report on the shocking fact that things were super-sexist in the “back then.” But oh, did CR’s heart lift after turning page the first. It’s hard to imagine a woman — or a teenage girl — who won’t love this book.

H"Unmentionable: The Victorian Lady's Guide to Sex, Marriage, and Manners," by Therese Oneill (Little, Brown)

The conceit is that the author, Therese Oneill, has had it up to here with the kind of dreamy-eyed young woman who’s always got her nose stuck in a Jane Austen novel and who wishes she could live her life not in the feminist here and now, but in that bygone era of “chivalry and honor, gilded beauty and jolly servants.” Oneill decides she will take one of these girls in hand and tell her some home truths. “Most of the things you love about the 19th century aren’t real, child,” she tells her. “They’re the creations of gracious hosts who tidy up the era whenever you visit through art, books, or film.”

She proposes an extended field trip to the era — which she expands to include everything from Austen through the Victorians — so she can reveal to her besotted pal the down and dirty truth about matters from menstruation to childbirth, clothing to cooking, social life to sex, and thus cure her from binge-watching the latest iteration of “Pride and Prejudice.” What a nasty world she shows her charge, illustrating it with advertisements, photographs and artwork of the period.

“Some would argue,” writes Oneill, that “the nineteenth century was one of the filthiest centuries in all of Western history.” City streets flowed with “sewage, rotting offal, and other garbage.” By 1860, the Thames was “visited by thousands of tons of fecal matter every day.” All of this filth accumulated on everyone, even the most dewey-eyed Victorian heroine. Her hair — waist length — was rarely washed and so greasy that it was a magnet for dust and soot. Bathing was infrequent and unpleasant. It often took the form of a cold water-and-vinegar sponge bath in a freezing bedroom: “Do not perform these ablutions in a warm room. It will lead to torpor, masturbation, and like everything else in the nineteenth century, consumption,” Oneill, a humorist and contributor to Jezebel, advises her readers.

Stink was a related problem. To the modern sensibility, even the most carefully turned-out Victorian — male or female — reeked. Heavy perfumes covered bodily smells; onion juice was a popular hair tonic; dental hygiene was primitive and certainly not concerned with freshness of breath. Households were poorly ventilated, so various cooking smells clung to fabrics and damp walls. The problems of chamber pots — also known as “jerries, night soil, commodes, slop jars, close stools and thunder mugs” — also contributed to this noisome mix. The section on these matters contains the ominous detail: “Food conditions were such that you were near guaranteed to suffer diarrhea on a household scale a few times a month.”

About menstruation, the medical literature of the time was filled with anxiety-producing theories; uneven menstruation was believed to cause hysteria, “a disease both powerful and not actually real.” According to one prominent male authority, light menstruation made a woman not only unfit to bear children but also “most ugly and hateful, especially to men, and often fairly insane against her husband; besides sending her think blood tearing through her brain, torrent-like to gorge, lacerate and soften it.” The flow of blood was stanched by, as Oneill puts it “anything that worked” — from baby’s diapers, sea sponges and bandages to prettily crocheted sanitary pads, all of which had to be washed and dried in near-secrecy, as no neighbor, and certainly no man, should ever see such shameful things.

The Victorian ideals of perfect womanhood would certainly be as onerous as the wretched daily battle to get dressed and stay somewhat clean. The young woman was expected to present herself as a jewel worth capturing and to never, ever pursue a man. Guidebooks on marriage frequently reminded men not to consummate the union with an actual rape, and the happiness of their shared home was largely her responsibility.

The book ends with a rousing reminder to the dreamy Austen fan of why the present is so much better for a young woman than the past: “You and I can wear pants. And run for president. And divorce men who hurt us. And do whatever work we want or need to do to make our lives as we want them.” It’s an ironclad argument for the modern era, but it leaves unanswered the central question the book prompts: Why has there been such a craze for novels, movies and television series about Victorian life among so many young women living in the pants-wearing, presidency-aspiring female here and now?

The popularity of these entertainments suggests something that has become almost taboo to assert in modern America: that the emotionally valuable center of a young woman’s life might be her search for the right husband, the creation of a strong marriage and the raising of the union’s children. Certainly we all know many young women whose future plans include these goals — but not to the exclusion of a career, of a vital sense of power and agency in the world outside home. That these stories take place in the past allows the modern young woman to read them — and to dream about their heroines — without conflict. Perhaps it is this stubborn, enduring and thoroughly non-liberated attraction to marriage, family and home that is the true “unmentionable.”

Unmentionable

The Victorian Lady’s Guide to Sex, Marriage, and Manners

By Therese Oneill

Little, Brown. 307 pp. $25