dave-mittlemanHand sanitizers are available nearly everywhere we turn: in daycare centers, at the mall, in bathrooms, at hospitals and in schools. The handy product has been proven effective in reducing the prevalence of hand-to-mouth infectious diseases. However, a study at East Tennessee State University recently revealed that some hand sanitizers might not be as good at killing bacteria as we once believed.

Scott Reynolds, a specialist in infection control at the James H. Quillen Veterans Affairs Medical Center accidentally discovered the problem with some hand sanitizers while giving a simple demonstration on the merits of hand washing to a friend’s class at East Tennessee State University. During his demonstration, Mr. Reynolds had the students place their hands on agar plates of growth medium before and after one of several experimental conditions: rubbing their hands briskly under tap water, sudsing with hospital-grade soap, or rubbing their hands with one of two alcohol-based hand sanitizers. One of the hand sanitizers was a version from a hospital and the other was one that Mr. Reynolds’ wife bought at a discount store. The next morning, the culture plates from the students’ hands who used the hand sanitizer from the discount store showed clumps of bacteria all around the handprints. Mr. Reynolds was puzzled, but soon realized his mistake in assuming both hand sanitizers would be equally as effective: the version from the hospital contained 62% ethyl alcohol while the version from the store contained only 40%.

Ironically, the science experiment at East Tennessee wasn’t meant to provide such impressive results. But while the study did start out as an informal classroom experiment, it turned into something much more after its publication in the journal of Emerging Infectious Diseases. Overall, Mr. Reynolds as well as other researchers studying the effectiveness of different methods of hand washing or sanitization warn consumers to check the label on hand sanitizers. To be effective, a hand sanitizer should contain at least 60-95% alcohol.