According to research published in the May issue of Applied and Environmental Microbiology, washing with contaminated soap from bulk-soap-refillable dispensers can increase the number of disease-causing microbes on hands and potentially increase the transmission of bacteria.

Bulk-soap-refillable dispensers where new soap is poured directly into a dispenser, are widely used, but compared to sealed-soap dispensers, which are refilled by inserting a new bag or cartridge of soap, they are prone to bacterial contamination and several outbreaks linked to the use of contaminated soap have already been reported in healthcare settings.

Researchers conducting the study found an elementary school where all 14 of the soap dispensers were already contaminated and asked students and staff to wash their hands, measuring bacteria levels before and after handwashing. They found that Gram-negative bacteria on the hands of students and staff increased 26-fold after washing with the contaminated soap.

All the participants' hands were decontaminated after testing by washing with uncontaminated soap followed by hand sanitizer. At the conclusion of the study, all the contaminated soap dispensers were replaced with dispensers using sealed-soap refills. After one year of use, not one of them was found to be contaminated.

Additional articles on this topic include:
Coming Clean On Hand SoapHand soaps can be easily contaminated, making them a "playground" for bacteria
Contaminated Hands?Study finds refillable soap dispensers can be breeding grounds for bacteria