Forearms and calves are often cleaned more thoroughly at bath time and have a greater diversity and potentially a healthier collection of microbes compared to the samples taken in oily hotspots behind the ears, between the toes and in the naval.

Skin behind the ears and between the toes can host a collection of unhealthy microbes, according to a new study by a team at the George Washington University. 

Researchers at the GW Computational Biology Institute wanted to take a closer look at the skin microbiome of healthy people. Marcos Pérez-Losada, an associate professor of biostatistics and bioinformatics at the GW Milken Institute School of Public Health, and his team were interested in testing what they call “the Grandmother Hypothesis,” which states that scrubbing behind the ears and between the toes may help keep the skin in those regions healthy,

Keith Crandall, Director of the Computational Biology Institute and professor of biostatistics and bioinformatics at GW, posited that these hotspots are normally washed less often compared to the skin on the arms or legs and thus may harbor different types of bacteria.

Pérez-Losada and Crandall designed an innovative genomics course and then unleashed a team of students to help them find out.  The 129 graduate and undergraduate students were taught to collect their own data–by swabbing certain moist and oily hotspots, behind the ears, between the toes and in the naval. They also collected samples from control dry areas like the calves and forearms.

The students then learned how to extract and sequence the DNA in the skin samples to compare the microbes living in the hotspots to those in the control regions.

 The researchers found that forearms and calves which are often cleaned more thoroughly at bath time had a greater diversity and thus potentially a healthier collection of microbes compared to the samples taken in the hotspots. 

If the microbiome tips in favor of detrimental microbes, skin diseases like eczema or acne can be the result, Crandall says.

This research, including an earlier study by the same team, is one of the first to look at the diversity of sites across the skin microbiome in healthy adult subjects and may  provide a reference point for future research. Crandall says the study of how the collection of microbes on the skin leads to health or disease is in the early stages.

The new study “Spatial diversity of the skin bacteriome,” was published Sept. 19, 2023 in Frontiers in Microbiology.