Little is fundamentally new about keeping clean and yet values shift constantly. Every age chooses its own place on the line between squalid and immaculate From her new book 'Clean' Katherine Ashenburg selects the major turning points in the story of hygeine.

1700 B.C. The world’s earliest known bathtub, found in the Palace of Knossos on Crete, is made of painted terra cotta.

500 B.C. The Greeks have public baths with tubs and primitive showers; at home, they wash in pedestal sinks.

100 A.D. The heyday of the great imperial bathhouses. Romans have transformed the daily bath, which includes cold, tepid and hot waters, into an elaborate, highly social daily interlude.

537. The Goths disable the Roman aqueducts, and the imperial baths never recover. Baths and bathing last longer in the eastern part of the Byzantine Empire, where the Roman bath mutates into the hamam, or Turkish bath.

1000. The Crusaders return from the east with the news of a delightful custom – the Turkish bath. Bathhouses are built all over Europe, and they flourish until

1347. The Black Death invades Europe, where it will kill one out of every three people within four years. Doctors warn that opening your pores in warm water allows the plague to enter the body. Bathhouses are closed and people shun water as much as possible for four centuries. This is Europe’s dirtiest period, when the traditional washing advice is "Saepe manus, raro pedes, nunquam caput"("Hands often, feet rarely, the head never.") As for washing the body, out of the question.

1762. Rousseau’s Emile, celebrating cold water and cleanliness, is published. The Romantic movement glorifies nature, and immersion in water makes a gradual return.

1829. Boston’s Tremont Hotel installs eight basement "bathing rooms where guests could wash themselves all over." An innovation that forever changes the hotel world.

1837. Queen Victoria ascends the throne, but has no bathroom in Buckingham Palace. She uses part of her dress allowance to have hot water piped into her bedroom, where she bathes in a portable tub.

1842. The Frederick Street Baths open in Liverpool, Britain’s first public bathhouse in a poor neighbourhood, and a prototype for Britain and the Continent.

1865. The success of the Sanitary Commission in the Civil War convinces Americans that cleanliness is progressive, democratic and quintessentially American.

1878. Procter & Gamble, in Cincinnati, launches Ivory, one of the first affordable toilet soaps. Toilet soap and the newish business of advertising grow up together and reinforce each other. By the end of the 19th century, soap and patent medicines have become advertising’s biggest customers.

1998. Seven hundred new antibacterial products are launched in America between 1992 and 1998. One of them is the "oral-care strip," antimicrobial tape designed to be stuck to the tongue.

2005. Almost one in four new American houses has three or more bathrooms. The average size of the American bathroom triples between 1994 and 2004.

2009. The increasingly respected "Hygiene Hypothesis" contends that our rapidly rising incidence of allergies, asthma and other illnesses is due to the over-cleanliness of the prosperous West

Clean: An Unsanitised History of Washing is published today by Profile Books price £8.99

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