Are Dogs’ Mouths Cleaner Than Humans’?

Young Scientist in Action
By The Bark Editors, September 2012, Updated February 2015
Abby Walling & Lucy

Are dogs’ mouths cleaner than humans’? Her grandmother said they were, her mother said they definitely were not. Not one to take things at face value, Abby Walling of Iowa City, Iowa, decided to conduct an experiment and answer the question once and for all. Not only did she reach a conclusion, she won a 2011 Young Naturalist Award from New York’s American Museum of Natural History for her work. As a bonus, she no longer feels guilty about letting Lucy, her kiss-happy Yorkshire Terrier, lick her face.

Specifically, Abby investigated the bacterial content of both human and canine tongues. She hypothesized that humans would have fewer bacteria — after all, they brush their teeth regularly and aren’t quite as indiscriminate as dogs about what they put in their mouths. She then obtained saliva samples from five dogs and their associated humans and plated the samples on agar in a laboratory. What she found surprised her: Humans do have more bacteria in their mouths than dogs. That, however, is only part of the story (to read Abby’s full project report and results, go to and look under Past Winners, 2011).

At the time, Abby was in the eighth grade at Northwest Junior High School, and this project landed her a place in the State Hygienic Lab’s student mentorship program, which matches junior high and high school students with a laboratory scientist mentor; Gabe Gerken, public health microbiologist, helped her refine her methodology and the lab provided testing supplies.

What does Abby see in her future? “After college, I’d like either to manage a zoo or conduct scientific research concerning animals and the environment. I am very passionate about improving the world, and I believe I can use research to solve some of the environmental problems the world is facing today.”

Sounds like we’re in good hands.

Article first appeared in The Bark, Issue 71: Sep/Oct 2012