What's buggier: beards or fur?

Which actually has more bacteria lurking inside: dog fur, or a human beard?
17 September 2019

Interview with 

David Williams, The Queen's Veterinary School Hospital




A shortage of veterinary scanners means machines for humans are increasingly being used to image our pet dogs, leading some people to wonder about infection risks. But which actually has more bugs lurking inside: dog fur, or a human beard? To sniff out an answer, we let Naked Scientists Ben McAllister and Ruby Osborn off the leash to investigate. In the interests of confidentiality, the names of some of the furry subjects in this report have been bleeped to protect their identities...

Ben - Recently, there's been a lot of hullabaloo about the relative cleanliness of dogs and humans with the study from the journal European Radiology finding that, on average, men's beard hair contains higher populations of bacteria than dog fur.

Ruby - That's interesting and a bit gross, but why was a study in a radiology journal we hear you shout?

Ben - And if they aren't shouting it, I certainly am. So please enlighten me.

Ruby - The study was initially trying to determine whether it was safer and/or cleaner to get an MRI...

Ben - Which is a common type of medical scan also known as a Magnetic Resonance Image.

Ruby - ...in a machine that was shared by both humans and dogs compared to a machine that was just used by humans?

Ben - Shared at different times I expect.

Ruby - Who's to say.

Ben - Well, what did they find?

Ruby - Ben, surely you remember that we contacted the study author, Dr Andreas Gutzeit to find out more. Sadly, Dr Gutzeit was not available for an interview but they found that the MRI shared by humans and dogs in fact contained fewer bacteria than the MRI only use by humans. The shared machine was carefully cleaned after every doggy patient meaning it actually got cleaned more often than the human only machines.

Ben - It seems that the conclusion of the MRI thing is that whether you've got humans or dogs in your scanner you should probably just clean it out regularly.

Ruby - Yep. But let's not gloss over their results about facial hair versus dog fur.

Ben - That's right. They swabbed dogs fur in 30 dogs and people fur in 18 adult men and compared the bacteria found in each.

Ruby -  Dr Gutzeit commented that the study showed that humans and animals are very similar and the paper explains that they actually found slightly higher populations of bacteria, on average, on the men's faces.

Ben - And the astute of us will note at this point that I know how to grow facial hair.

Ruby  - And I know how to test for bacteria.

Ben -  So given this shows called the Naked Scientists and not just the naked people who talk to you about stuff, we went to the Queen’s Veterinary School here at Cambridge University to see how I compared to a dog.

We’re here with…

David - David Williams. I'm veterinary surgeon here.

Ben - And well, who else is with us Ruby?

Ruby - I have my two test subjects. I have beep, the black labrador and also Ben and Australian man.

Ben - And we are going to find out who's got more bacteria. David, who do you think is going to have more bacteria in their hair? Do you think it's going to be beep here or do you think it's going to be me?

David -  Well, I would have thought it would be beep, because beep doesn't wash herself on a daily basis, and I hope that you might.

Ben - That makes some sense, but I guess, proof is in the swabbing, so let's get down to it shall we.

Ruby - I'm going to swab beep's neck. Come here darling, there we go. Good girl.

Ben - Okay. One sample down... And swab number two -  I'm very nervous about this one...

Okay, all done.

Ruby - As well as Ben's beard, I also swabbed his hairless cheek to see if it's really the beard that's the problem or just human's faces.

Ben - And we made one more stop at the Animal Hospital's MRI machine to see how clean that was?

We are here in the radiology department with...

Mari - Mari Ode.

Ruby - So how often do you clean your MRI machine?

Mari - We'll be cleaning our MRI machine between every patient, and at the end of the day we’ll be giving it another clean.

Ben - Right. So that sounds  quite clean and I'm expecting it's going to have less bacteria than I'm gonna find a human MRI machine which, apparently, aren't cleaned all that thoroughly all the time. You work with animals quite a lot I expect?

Mari - Yeah, every day.

Ben - All kinds of different animals or?

Mari - All kinds, every sort of species. Our main species are cats and dogs but we will have all sorts. We've had tigers, we've had many cheaters, we've had lots of different animals.

Ben - And, so given your vast experience of different animals, who do you think is going to have more bacteria on their face? Do you think it's going to be beep, the black Labrador who we swabbed or do you think it's going to be me, a 25 year old human man?

Mari - Uh, oh. I think the interesting question will be, also, what kind of bacteria? Do you have more dangerous bacteria or do you just have more as a human being compared to an animal?

Ben - I did wash it this very morning.

Ruby - I was about to ask if you'd washed your beard.

Ben - Well, I suppose only time will tell. So were about to swabbed the MRI machine.

Mari - And this is the coil that the animal sits in.

Ben - It sounds like they clean that thing a good deal?

Ruby - Yep. And that was supported by our swab results which showed a very low levels of bacteria.

Ben - Our doggy helper also showed low amounts of bacteria, actually lower than any of the dogs in the original study.

Ruby - And then there's Ben...

Ben - Oh dear.

Ruby - Ben's beard did in fact contain high levels of bacteria. Five times more than the moderate amount on his cheek.

Ben - Even though I'd just washed it that morning!

Ruby - So it seems our little experiment...

Ben - Which is not very rigorous, by the way, with just one person and one dog.

Ruby - Stop trying to get out of it Ben! Our little experiment supported the paper's findings that human beards contain more bacteria than dog fur. A secondary aspect of the study that was in addition to having a higher density of bacteria overall, the density of human pathogenic bacteria, or bacteria that can harm humans was slightly higher in men than in dogs.

Ben - It's important to note that the secondary result of this paper didn't reach what is called "statistical significance," which means it wasn't clear from the data that human hair does contain more harmful bacteria than dog fur, and we can't really draw that conclusion with any confidence. That being said, even if it is true, perhaps it's not surprising then humans carry more human-related bacteria than dogs given we're well -  humans.

Ruby -  There's also the question of if bacteria being present in dog fur or human fur is really that big of a problem to begin with?

Ben - Bacteria are everywhere.

Ruby - Keyboards.

Ben - Phones.

Ruby - Doorknobs.

Ben - Handrails.

Ruby - You get the idea. Whether or not bacteria are denser in human beard than in a dog's fur, a beard is probably not the only bacteria dense in you'll come across in your day-to-day life.

Ben - The study authors even said there's no reason to believe that women may harbour less bacteriological load than bearded men. So leave us beardies alone! We are no worse than the rest of you.

Ruby - Yep. Beards are fine. You should probably still wash them regularly though.

Ben - I do!

Ruby - Well then, it's fine.

Ben - Some would say - cool - even.

Ruby - Some might, although our research found no evidence to support that assertion.

Ben - Oh!


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