The thought of a daily shower would have filled the 17th century Frenchman with fear. To splash away with abandon, to open your pores and leave your body vulnerable to all that disease, would be practically asking to get sick. In fact, our bathing habits would have disgusted him, much like his habits disgust us: never washing his body with water or soap, for instance.

Or changing his linen shirt to get clean.

How cleanliness has changed in the West is the engrossing (and sometimes gross) subject of Katherine Ashenburg's"The Dirt on Clean: An Unsanitized History," which skates merrily from ancient frolics at the public baths to today's obsession with hand sanitizer and teeth-whitening strips. Ashenburg, whose previous book was a popular history of grief called"The Mourner's Dance: What We Do When People Die," argues that contemporary cleanliness has more to do with appearances than hygiene. Considering our relative lack of physical exertion compared with our ancestors, why do we consider a daily shower an ideal, anyway? Apparently, the less we sweat, the more we clean. But our very fear of dirt may actually be making us sick.

Salon spoke with Ashenburg by phone from her office in Toronto.

What did clean mean in ancient Rome?

If you were a man, you would take off all your clothes, put a little oil on your body, rub it with dust and go out into the playing field to work up a sweat. Then you would get somebody to scrape off your perspiration with an instrument that looks like a little tiny rake, called a strigil. Then you would get into a tepid bath, then into a really hot bath, then into a cold bath.

You never used any soap, and it was all done in public. If you were just a normal person, you'd probably spend a couple of hours every day in the bathhouse, where you could get wine, food, sex, a medical treatment, a haircut. You could have a depilator pluck the hair in your armpits.

Why wasn't soap popular?

Soap was a combination of animal fat and lye. The Egyptians went to great lengths to make a soap that was mild enough to use on bodies, but many cultures, including the Romans and Greeks, didn't really. So they scraped themselves. Basically, it was a kind of drastic exfoliation. They probably got as clean as soap makes you. Most people, except very rich people, didn't use soap until about the second half of the 19th century.

Why did public baths go out of fashion?

They went out of fashion because the infrastructure to run them -- the mechanisms that brought them water, that heated their water, that separated out the different heats of the various pools -- required an enormously sophisticated and complicated infrastructure, which the Roman Empire had. But when the empire started to fall apart, people couldn't maintain that, and the invading barbarians disabled the aqueducts. There was never an empire large enough to support that again. ...