10 'Harmless' Things You Should Really Wash Your Hands After Touching

Pencil Sharpener Handle
Sharpened pencils are deeply satisfying. Consider an electric sharpener if you're wary of meeting microbes on a manual one. Hemera/Thinkstock

In 2009, Charles Gerba was at it again. This time, he teamed up with research scientists Kelly Bright and Stephanie Boone to see if disinfecting wipes could help control the spread of infectious diseases in elementary school classrooms. Their study focused on six classrooms in one Seattle school. Three of those rooms were part of the control group and received no intervention. The other three were thoroughly cleaned each day by parent volunteers who scrubbed 12 test surfaces with disinfecting wipes containing quaternary ammonium, a chemical compound often used in disinfectants, surfactants, fabric softeners, antistatic agents and wood preservatives [source: Bright et al.].

Over seven winter weeks, the scientists swabbed the test surfaces in both the control and experimental classrooms several times. They sent the samples to a lab, where they were analyzed for the presence of bacteria and viruses. Their results confirmed what we already know from the first entry on our list: Water fountain buttons were hotbeds of microbial activity. Surprisingly enough, the next most contaminated object per square centimeter in the classroom was the manual pencil sharpener handle. The least contaminated objects were the classroom entrance and exit doorknobs. How was this possible? Gerba and his colleagues noted that the doors in the classrooms were usually propped open, so they escaped being touched throughout the day. The pencil sharpeners weren't so lucky. Kids used them constantly and, as a result, left behind more than just a few graphite shavings [source: Bright et al.].