Even where there seem to be similarities between cultures, they vanish on inspection. In the Roman empire, the baths were the hub of social life. Often palatial, they incorporated club rooms and libraries as well as heated pools. It sounds like an exceptionally well appointed modern community centre, until you reflect that the sexes bathed together naked, and would expect to be washed by servants rather than washing themselves. Our concept of personal and bodily privacy had not yet evolved, and that puts Roman civilisation beyond our understanding, however hard we try to imagine it. Also odd, for us is that the Romans never washed with soap, though it had been known from Babylonian times. Instead they scraped their bodies with a metal blade called a strigil, then rubbed them with oil. Just reading about it makes you itch. The mixture of sweat, dirt and oil scraped off famous athletes and gladiators was sold to their fans in vials. Some Roman women used it as face cream.

 

Early Christians reacted sternly against Roman cleanliness, perhaps because they associated the baths with hedonism. Saints embraced filth with ardour. St Agnes never washed at all in her admittedly short life; St Godric walked from England to Jerusalem without washing or changing his clothes. Jesus had set them an example. He shocked the Pharisees by not washing before meals and flouted purity laws by touching a corpse and a leper. Holy hermits who sat on heaps of their own ordure may seem to have taken things a bit far, but their realisation that it is inner cleanliness, not outer, that matters helped Christianity to change the world.

 

What we now think of as a Turkish bath, Ashenburg points out, is really a Roman bath. When the Goths overran the western empire, the traditional baths survived in the east, and were rediscovered by the Crusaders, who brought back the good news to medieval Europe. Their stories of plentiful hot water, relaxation and sex proved irresistible and, by the 14th century, London had at least 18 public bathhouses. Because you stewed in them, they were called "stewhouses", which, shortened to "stews", became the name for a brothel. That, too, followed Roman practice, which had housed prostitutes in or conveniently near baths. English medieval bathhouses did not, it seems, allow naked mixed bathing, but the Germans and Swiss did, and attracted scandalised foreign observers.

 

It was not a sudden onset of decency that closed the bathhouses, however, but terror. Beginning in the mid-14th century, bubonic plague, called the Black Death, killed 25m Europeans, a third of the population, in the most devastating pandemic the world has yet known. As was usual with natural disasters, it was attributed to the Almighty's disapproval

 

of luxury, including bathhouses. But science came down on the same side as religion. Medical authorities opined that warm water, by opening the pores, let in disease, so should be shunned. All over Europe the shutters went up at the baths, and washing fell into disrepute for four centuries, among high and low alike. James I was reported to wash only his fingers, and a survey of hundreds of French etiquette manuals from the 16th to the 18th century has found they unanimously recommend washing just hands, face and hair. The resultant smells were jauntily accepted. "I take after my father," boasted Louis XIII of France. "I smell of armpits."

 

A theory developed that wearing a linen shirt, and changing it often, was better and safer than washing, because it soaked up the sweat. Louis XIV changed his three times a day. But for the timorous, even this was too much. Boswell records that the 18th-century Marquis d'Argens wore the same flannel under-waistcoat for four years, for fear of catching cold. When the king eventually persuaded him to change it, pieces of his skin came away with the cloth. In Islam, cleanliness had always been an important religious requirement, and 17th-century travellers brought back reports of strange peoples who washed their genitals and took a bath three times a week. Under the Spanish Inquisition, a damning piece of evidence levelled against Moors and Jews was that the accused were "known to bathe".

 

Washing made a comeback in the later 18th century. The age of revolution and romanticism valued simplicity and naturalness, and water — in the form of mountain torrents and medicinal springs — became fashionable. Rousseau recommended bathing children in ice-cold water, winter and summer, and a sophisticated clientele sought to relieve its frayed nerves and overtaxed digestions by taking the waters at spas. John Wesley, the founder of Methodism, who invented the phrase "Cleanliness is next to godliness", wrote a manual claiming that cold baths had been known to cure blindness and leprosy, as well as "hysterick cholik" in ladies.

 

Charles Dickens took a cold shower every morning, and declared that it was "a positive necessity of life". But for the Victorians, washing became a class-divider. Thackeray called the poor "the great unwashed", a description, Ashenburg notes, that would have applied to the whole population a century earlier. The new idea that the poor were dirtier than the well off lasted well into the 20th century. George Orwell remembers having it drummed into him as a child that the working classes smelt. Their custom of keeping coal in the bath dates from the same period.

 

Ashenburg, a Canadian, rounds off with a splendid diatribe against American supercleanliness, which, like every section of this book, is full of acute perceptions. At first, as she sees it, a common standard of cleanliness was a way of unifying America's immigrant masses. The wash houses at Ellis Island were designed to shower 8,000 every day. But now, cleanliness has become a market force. The intimate-hygiene sector prospers by preying on social and sexual insecurity, especially of young women, convincing them that it is vital to eliminate every trace of the body's natural smells and secretions, and to have preternaturally white teeth, even though dentists fear that whitening strips (introduced in 2002 and currently a $500m industry) damage gums and enamel. Quite apart from the anxieties these pressures cause, there is something sinister about the most powerful nation on earth shunning the natural and human as unacceptable, and opting for the illusion that they can control every aspect of their lives.

 

To a grubby old-style British reader, all this makes good sense. The only possible complaint about Ashenburg's exceptionally enjoyable book is that, being beautifully designed and illustrated, it is not suitable for reading in the bath. Available at the Sunday Times Books First price of £11.69 (including p&p) on 0870 165 8585 and timesonline.co.uk/booksfirst