Anti-bacterial soap doesn't work, according to a new study.

"We didn't see any difference in the numbers of bacteria (on the hands) with plain soap as with antimicrobial soap," Elaine Larson told CBC Radio. Larson is the associate dean of research at the Columbia University School of Nursing.

Larson's team followed 238 housewives in New York City. Half of them got anti-microbial soap for daily hand washing and the other half was given plain soap. The soap wasn't labelled.

Researchers discovered both groups had fewer germs on their hands after washing, but there were no differences between the two groups.

Soap and water work by washing away germs. Larson says for daily hygiene, hand-washing with regular soap is fine.

She also warns that heavy use of anti-microbial soaps could add to a new breed of hard-to-kill bacteria, but they are useful in some circumstances.

"If somebody in your family has a cold or diarrhea or if you have an older person in your home...or somebody with cancer, than I'd say you could use the (anti-microbial soap)," said Larson.

Larson says anti-microbials are good for preventing skin infections and several studies have proven that.

"Nobody really knows how much bacteria you should have on your hands anyways...it's normal to have up to 10 million on your hands. That's not unhealthy," said Larson.

Larson says the purpose of handwashing is to prevent "cross-contamination" — when you're changing a dirty diaper or shaking hands with someone who has a cold and you don't want those germs.

She recommends the best prevention against "cross-contamination" is the alcohol-based hand sanitizers available at your drugstore.

"They kill more germs faster than any kind of soap."