Liquid soap in bulk, refillable dispensers can become contaminated and actually increase the number of disease-causing microbes when people wash their hands with it, according to research published in the May issue of the journal of Applied and Environmental Microbiology.


Refillable dispensers are common in public restrooms, the researchers said, and outbreaks linked to contaminated soap have been reported.

Sealed-soap dispensers, the kind refilled by inserting a new bag or cartridge of soap, are a better choice — they’re less prone to bacterial contamination.

The study was conducted by scientists from GOJO Industries in Akron, Ohio; BioScience Laboratories in Bozeman, Montana; and the University of Arizona, Tucson who found an elementary school where 14 soap dispensers were contaminated.

Students and staff were asked to wash their hands with the soap, and bacteria levels were measured before and after hand washing. The researchers found that Gram-negative bacteria on the study participants’ hands increased 26-fold after they used the contaminated soap. (All the participants’ hands were decontaminated after testing.) 


“This is the first study to quantitatively demonstrate that washing hands with contaminated liquid soap actually increases the number of Gram-negative bacteria on hands.  Furthermore, the results directly demonstrate that bacteria from contaminated hands can be transferred to secondary surfaces,” lead researcher Carrie Zapka said in a news release.


After the study was concluded, the school’s contaminated soap dispensers were replaced with dispensers using sealed-soap refills.  After one year, not one of them was found to be contaminated.


A copy of the research article can be found online here.