Science has shown over and over again that bar soap does not transmit infection. It is a powerful, plastic-free, and cheap disease-fighting tool.
Switching from liquid soap to bar soap is an easy and effective way to reduce one's plastic use over time. The only problem is, many people believe that using bar soap can transmit infection. There's a tendency to think that, since everyone is using the same bar of soap, and who knows where their hands might have been, the soap can somehow pass around infections; but the New York Times explains in a recent health column why this is not the case.
Several studies have examined this question, with the first and most in-depth experiment happening in 1965. Scientists coated their hands with approximately 5 billion bacteria, including disease-causing strains of E. coli and staph. Dr. Richard Klasco explains:
"The scientists then washed their hands with a bar of soap and had a second person wash with the same bar of soap. They found that bacteria were not transferred to the second user and concluded: 'The level of bacteria that may occur on bar soap, even under extreme usage conditions (heavy usage, poorly designed non-drainable soap dishes, etc.) does not constitute a health hazard.'"
A second major study in 1988 inoculated bars of soap with pathogenic bacteria to see if it could be transmitted to soap users, but test subjects had no traces of the bacteria on their hands after washing. Subsequent studies have continued to show the same results, while underscoring bar soap's powerful ability to fight serious infections, such as Ebola.
One commenter on the NYT article gives further background as to why the bacteria does not stick to a bar of soap:
"The bacteria can't evolve high levels of resistance because the effect of soap depends on a chemical property -- the hydrophobic effect, which is the fact that in the absence of a detergent, oil won't mix with water -- that is essential for the functioning of nearly everything in a cell: its membrane, its enzymes, its DNA. The only way a bacteria could evolve high levels of resistance would be to totally restructure almost every component that it is made of."
Liquid soap, to be fair, is not teeming with bacteria either. The stuff works, even if the dispenser is icky and you can avoid touching it after washing your hands, but the point is that it's not any better. So, if you can avoid the added plastic from all those bulky dispensers (a rough estimate of 270 million plastic pump bottles go in the trash annually and most are never recycled), and the added cost (people use 7 times more liquid soap per washing than bar soap, and it's a more expensive product to begin with), then why not give bar soap a try?