In ancient Rome, people smeared themselves with pumice or ash to clean their bodies. Then, they'd layer on some oil.

"If the kids got kind of messy in the backyard, basically Mom would get out some olive oil and kids would rub it over themselves and then scrape it off," said Robert Cohon, curator of art of the ancient world at The Nelson-Atkins Museum of Art in Kansas City, Missouri.

Rome was known for its public baths, Cohon said. But you'd go for a spa soak to be social. Cleanliness wasn't really the focus.

"One gets the sense that there are different attitudes toward hygiene in the ancient world than what we have today," he said.

Soap science

Without soap, you can only get so clean. But those who used ash and olive oil were on to something.

Basic bar soap begins with animal fat or vegetable oil. You add an ingredient that both dissolves in water and cuts through grease, such as ashes. Then a chemical reaction happens to make soap.

Gunk, like dirt or germs, sticks to our hands because of the oils on our skin. Soap molecules grab onto oil particles. Then water washes the gunk away. If you use enough soap--and rub your hands together for long enough-- you'll have less oil and germs left on your hands.

That's why public health officials are always trying to get us to wash our hands for at least 20 seconds.

Plain soap doesn't kill bacteria, but microbes get flushed down the drain.

Personal preference

Still, lots of U.S. consumers think bar soap is covered with germs after you use it, according a recent poll from the Mintel, a global market research firm.

These days, when it comes to cleanliness, there are lots more choices including body washes, foams and liquid soaps.

"The market for bar soaps is declining," said Frauke Neuser, principal scientist with Procter & Gamble's Olay Skin Care. "Probably about two percent over the last five years. But it is definitely declining."

P&G—the home of Ivory Soap--has been making and selling soap since the 1830s.

Neuser says more people, at least in North America, are opting for liquid soaps or body washes over bar soaps. But it's not really the gross-out factor that's driving down bar soap sales, she says. It's more about personal preference and how people want to experience getting clean.

Is it sanitary?

In our informal survey of visitors to the Kansas City Folk Festival—liquid soap was the definite crowd favorite.

One person said, "It just makes me feel cleaner." Another said, "Seems a little bit more sanitary." One person was grossed out by that nasty ring that bar soap leaves around the tub.

But is liquid soap somehow cleaner than soap in a bar?

Allen Greiner, a professor and vice chair of the department of family medicine at the University of Kansas Medical Center, was working at a pop-up clinic at the music festival. Greiner and his colleagues staffing the clinic were using lots of alcohol-based hand rubs. But for the rest of us, should it be bar soap or liquid soap?

"The truth is... there's probably not a real big difference," Greiner said.

By email, the Centers for Disease Control and Prevention said: "CDC does not have a recommendation for using bar soap or liquid soap over the other in a community setting...We are not aware of data to suggest that liquid or bar soap is more effective when used inside the home."

"You can get some bacteria that will stay on a bar of soap," Greiner said, "but by and large, when you use that bar of soap, all those bacteria are going to be washed away with the water that's flushing things out."

"I don't think there's any major reason to feel like it's icky."