Cleanliness is close to science

We all do it. We should be doing it several times a day. We don’t really think about it when we’re doing it. All we know is that we have to do it because if we don’t it leads to disease. I am of course talking about hand washing, or were you thinking of something else?! But in our mindlessness (and in our desire to hurry back to that ever important meeting or document you have to write because of that deadline) we do it quickly and ineffectively. So actually you are washing and drying your hands oh so very wrong! It turns out science has a thing or two to say about it.


It’s not just our internal microbiome that we carry but an external one; a cloud of bacteria, fungi and viruses haloes us. We all have our own individual yet invisible ecosystem that we leave on everything we touch. No two people will ever have the same “cloud” as mutations in the microbial species changes that frequently. Subtle changes do occur in our own “cloud” though but they are quite insignificant that even after two weeks, we could identify an individual from what they leave on a computer keyboard! We leave these traces on others, on our pets and in our homes. A nice infographic from the Scientific American shows how the microbial landscape of a home differs between how many men and women live in it and whether you have pets. Follow the flowchart to find out what lurks in your home.


There is a striking difference of bacterial species and diversity between men and women. It turns out that women have more bacterial diversity and more bacteria on their hands compared to men. This is despite the fact that women wash their hands more often than men. A team by the University of Colorado, Boulder, USA took swabs from students as they came out of their exams. Everyone carried a few species in common: Streptococcus, Staphylococcus and Lactobacillus and interestingly any two hands (even if they belonged to the same person) only shared 13% of all bacterial species found. They found that after washing it takes time for bacterial diversity to recover and there were even some species that preferred clean hands. So why are there differences between genders? It could be down to sweat, sebum production, hormones or perhaps that women use cosmetics. What can be said is that men’s skin is more acidic and this reduces microbial diversity. This will undoubtedly make everyone wash their hands a bit more after that professional handshake! Shockingly, in one study conducted by researchers at the University of Birmingham Aston it was found that both men and women have a harmful bacterial species under their nails: Enterobacteriaceae can cause diarrhoea and vomiting! Yuck! OK, so how should you wash and dry your hands?


First off wet your hands then get enough soap to cover them. Follow the instructions in the diagram in this link that redirects you to the IFLS page. This is the method that doctors and nurses use. A team from the University of Glasgow Caledonian found this method much more effective than the simple method we use every day. Consequently, the World Health Organisation formalised this method. Drying your hands is also something to be wary of. If you rub your hands in a hand dryer, this brings the bacteria from your pores to the surface of your skin. It is far better to wipe or scrub your hands with a paper towel as this reduces skin bacteria by 50% compared to just washing. If you don’t dry then it is reduced by 37% and if you rub in a machine it is reduced by only 18%. If you happen to not have paper towels to hand and there are only hand dryers, whatever you do don’t use the noisy jet dryers such as the Dyson Airblade. Apparently they fling viruses into the air up to 3 metres. This is in contrast to warm air hand dryers that fling up viruses to 75cm and paper towels that them fling up to 25cm. This makes me want to stay far away from them as much as possible! So using paper towels or a wad of toilet roll is the far better option compared to using hand dryers or not drying at all and which is why I always dry my hands. I see a lot of women that don’t dry their hands, if they only knew….!


Finally if you are on the go and can’t wash your hands, make sure you limit the use of hand sanitiser. It contains triclosan that kills off the good bacteria making it easier for antibacterial strains to flourish. They also increase your skin’s absorption of bisphenol A (BPA) which disrupts our hormones and can lead to hormone disorders, heart disease, cancer and developmental disorders in children. BPA can be found in food containers so if you do use it, limit the plastics you touch and especially those that contain food otherwise you’ll get a double dose of BPA, first through your hands and then your mouth.


So now you have your method sorted make sure you wash and dry appropriately especially in the winter time. It is how to prevent getting a cold after all! If you have a new born baby and you are keeping them inside until they get their own immune system, then you yourself will need to wash your hands effectively so as not to pass on anything. Clearly it is not just doctors and nurses that need to wash and dry hands effectively. It is time to get clean the scientific way.

Danae Dodge

I received my PhD in Scientific Archaeology from the University of Sheffield in 2011 which specialised in ancient DNA and anthropology. For my profile, see my websites: I started getting involved in Science Brainwaves as a volunteer in 2010. I have volunteered at presentations, events (such as the British Science Festival in 2011) and even participated in the Science is Vital protest march in October 2010. My first blog for Science Brainwaves was "Ancient Humans: Who were they? And who got it on?" which was the written version of a talk I gave for the Natural History Society at the University of Sheffield on 5 December 2011. I also have a public engagement page dedicated to ancient DNA, which I encourage both the public and specialists to join: