Clean: An Unsanitized History of Washing
by Katherine Ashenburg
358pp, Profile, £12.99

"The scent of one another's bodies was the ocean our ancestors swam in," Katherine Ashenburg writes wistfully in this entertaining tale of changing attitudes to cleanliness; whereas now, "smelling like a human is a misdemeanour, and the goal is to smell like an exotic fruit". Cocooned in our iPodded cells, deodorised and anaesthetised, we are fixed on privacy, and our bodies worry us. We don't really like admitting they exist. So Napoleon's instructions to Josephine - "I will return to Paris tomorrow evening. Don't wash" - seem alien, even absurd. In our age, the big money's on any product that can obliterate the whiff of female genitalia.

Yet we're still curious about what goes on in bathrooms - so curious that, according to Ashenburg, a new hotel has opened in Montreal featuring peep-holes between the bedroom and bathroom areas, giving guests a "voyeuristic opportunity" to get a good look at each other on the can or in the tub. Soon there will be no refuge for those, like Portnoy, struggling heroically to monopolise the only lockable room in the house.

Our current squeamishness is far removed from the Romans' take on the body. For them bathing was a highly social activity, with hours spent every day wallowing naked in pools of differing temperatures. There they would eat, talk and cavort with friends, business associates and prostitutes, before being scraped and oiled by an obliging slave. Gibbon attributed the Romans' downfall to all this bathing, but the British have always been wary of a good soak. I got here 30 years ago and am still searching for a satisfactory shower.

What with water shortages and the lawless profiteering among water companies, we may all have to resort to the sponge-bath soon. So here's some 1860s ablution advice: after your cold and meagre 2in-deep sponge-bath, "choose some object in your bedroom on which to vent your hatred, and box at it violently for some 10 minutes, till the perspiration covers you. The sponge must then be again applied to the whole body." (What the 19th-century Englishman really hated was hot water.)

I know someone who makes Charlotte Corday dolls - but Marat's demise was clearly not the ad for bathing that Archimedes's "Eureka!" moment was. The French have failed to impress anyone on the bathroom front ever since, preferring the shabbily romantic boudoir approach to the puritan, paranoid and patriotic American bathroom, a "laboratory" or "factory for washing". American anxiety about the body has always outstripped mere European disquiet. The average size of the American bathroom has tripled since 1994, Ashenburg tells us, with rich Americans now coveting more than one bathroom per person - literally giving themselves permission to shit in two places at once. What does that say about a society?

To differentiate themselves from Jews and Muslims, early Christians decided to be dirty: one sign of sanctity was to spend a good bit of your time writhing in excrement. Devout Jewesses have probably on average been cleaner than anybody, being guaranteed at least "12 serious baths a year", by way of the mikveh (without which menstruating women aren't allowed back in the synagogue).

But everybody in Europe was actually bathing quite a bit, publicly too, until the plague put people off it for 400 years. By the end of the 16th century, "To immerse yourself in hot water, you had to be foolhardy, German - or ill." German bathhouses remained open during episodes of the plague in the belief that the waters were therapeutic. (Later, Stuttgart's bathhouse even had a bath for dogs. How willingly they frequented it is not revealed.)

For some time everybody just changed their shirts a lot. Linen was held to have sufficient cleansing properties - cloaked in a clean chemise, you only needed to dip your fingertips in a bowl of water once in a while. Despite having vowed to live simply, Rousseau found it impossible to relinquish his 45 Venetian shirts. A thief finally freed him from his "servitude" to fine linen.

Thanks to the discoveries of Florence Nightingale, big advances in cleanliness were made during the American civil war - only three soldiers died of disease for every two that died from war wounds (half the number in the Mexican-American war). And the first world war led, among other things, to the invention of Kotex, an unadventurous name based on the words "cotton-like texture". Originally designed as throwaway bandages for American soldiers in France, it turned out all the nurses were using them too.

The book is full of such tidbits, often revealed in the form of sidebars and a great array of images, such as giant engravings of plumbing pipes. But Ashenburg really warms to her subject when she considers the disastrous effects of soap and deodorant advertising: the resultant body phobias may have caused the recent surge in asthma, allergies, arthritis, Crohn's disease and multiple sclerosis. We got too clean! She quotes Allen Salkin in the New York Times: "The same places where Americans most fear terrorism - airplanes, schools, mass transit, water supplies and computers - they also fear germs."

Our perplexity about cleanliness seems unresolvable. The Greeks considered bathing in hot water effeminate, and it has often been associated with vanity and lasciviousness. Only women get a bath in European painting: Rembrandt's Saskia, the harems of Ingres, Degas's sweaty whores and ballerinas, Bonnard's recumbent, waterlogged forms. All-male nude swimming in cold watering holes is considered much more excusable, and is sometimes acclaimed as a sign (or a test?) of virility. George Costanza (of Seinfeld) would disagree, being fearful of "shrinkage". How vain is that?

· Lucy Ellmann's Doctors and Nurses is published by Bloomsbury