Can a bar of soap transmit diseases?

Are there any health risks to using a communal bar of soap in, say, a health club?

No. Bar soap does not appear to transmit disease.

The most rigorous study of this question was published in 1965. Scientists conducted experiments in which they contaminated their hands with about 5 billion bacteria. The bacteria were disease-causing strains, such as staph and E. coli.

The scientists 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 nondrainable soap dishes, etc.) does not constitute a health hazard.”

In 1988, scientists employed by a soap manufacturer confirmed these findings. They inoculated bars of soap with pathogenic bacteria, in this case E. coli and Pseudomonas, and had 16 people use the bars. None of the subjects had detectable bacteria on their hands.

Studies since then have documented the presence of environmental bacteria on bar soap, but none have shown it to be a source of infection. Recent studies demonstrate the ability of simple bar soap to combat infection, even during outbreaks of serious infections such as the Ebola virus.

But would a jar of liquid soap be a better bet than bar soap? Scientists with conflicting proprietary interests jousted about the putative benefits of liquid soap versus bar soap beginning in the 1980s. But the Centers for Disease Control and Prevention, which recommends hand washing as the primary defense against infection, gives the same endorsement to bar soap as it does to liquid soap.

The only mistake one could make would be to fail to wash one’s hands because of an unfounded fear of contamination.