Grandma might have been right all along when she warned you to clean behind your ears and in between your toes.

Scientists at George Washington University in Washington D.C. theorized these spots would be a haven for bacteria, because they do not get washed as often as other parts of the body, like arms and legs.

Keith Crandall, professor of genomics at the university, recalled his own grandmother always telling him to ‘scrub behind the ears, between the toes and in the belly button.’

Under Professor Crandall, 129 graduate and undergraduate students swabbed themselves behind the ears, toes and in their belly buttons.

They did this every January in 2019, 2020, 2022, and 2023, skipping 2021 because of the Covid pandemic.

The team also swabbed their forearms and calves as control areas.

They extracted and sequenced the DNA in the skin samples to compare to microbes, microorganisms such as bacteria, living in the supposed hotspots compared to the control regions. 

Researchers found there was a greater diversity and therefore potentially a healthier collection of microbes on the forearms and calves, compared to the other areas. 

A healthier collection could point to more bacteria types that are less likely to cause disease. 

Behind the ears, in between toes and in belly buttons are often more moist and warm, giving bacteria the perfect place to thrive.

When certain bacteria take over the microbiome – the collection of bacteria, fungi and viruses throughout the body – they can shift the balance away from health, Professor Crandall said.

If the microbiome tips in favor of detrimental microbes, it can lead to skin diseases such as eczema or acne.

The microbiome varies across the body and will consist of bacteria that is both helpful and potentially harmful.

However, this can be avoided if the areas are cleaned thoroughly, just like your grandmother always told you to do.  

The study was published last month in the journal Frontiers in Microbiology.