Spar-Klean Science – Is the loo really cleaner than the dish cloth?


I need to be honest and say I am posting this against my better judgement.  I mean, no one is going to want to eat at my house if the cloth we use to clean the dishes is actually dirtier than my loo!  That said, ‘dirty’ may be a misnomer here because we all know that bacteria outnumber us by millions to one; that there are ‘good’ bacteria and ‘bad’ bacteria and, therefore, not all bacteria poses a danger to our health.

This test, which was growing in my bathroom (erk!), only grows the microbes.  And whilst differentiating between fungal growth and bacterial growth shouldn’t be too hard, actually identifying which bacteria is present in the samples is way beyond my own capabilities.  So theoretically, if there are many more bacteria in my dish cloth than my loo I could console myself (ie kid myself) that those type of bacteria are of the harmless persuasion, unlike the nasties which I am certain grow in my toilet.  Still, it doesn’t pay to ponder upon the results.  Ignorance is bliss, and all that.

We are currently learning about bacteria.  During our research we came across this article from the Daily Mail (yes, I do realise the Daily Mail is not an authority on germ theory), which references a study done in Arizona by a top microbiologist claiming that the dish cloth is the dirtiest house hold item, being dirtier than even the toilet.  I thought this would be a fun (!) experiment for the children to try out.  So we quickly got together to make up some agar and raided every science set we have ever owned to retrieve all the petri dishes we could.  Agar is a nutritional medium which encourages microbes to flourish.  It is so simple to make and frankly far too much fun was had with this project!  All you need is gelatine and bouillon:

Ribbet collagebac1
# it is vital that both the gelatine and bouillon is completely dissolved before pouring into the petri dishes#

As soon as they were poured in we placed the lids onto the petri dishes to ensure they remained as sterile as possible.  Both bacteria and fungi are present in the air, as we found out when we attempted to make a sour dough starter using natural yeasts in the air.

Unfortunately, we did not have enough petri dishes to use the same size throughout all the experiments I had planned.  But we did the best we could with what we had.  We used the smallest petri dish as our control, and the two largest to compare the microbes found on the loo and dish cloth.

We used a clean ear bud to swab first the dish cloth and then the loo:

Ribbet collagebac2

Using a zigzag motion we gently rubbed the bud over the surface of the agar, trying our hardest not to break through it.  We replaced the lid, labelling them using a permanent pen and turned the petri dish upside down to prevent condensation:


Before I share the results I want to give you some back ground to our cleaning routines.  We have used a bleach spray on the loo (and the rest of our bathroom) twice a day for the past couple of years.  Our kitchen cloth is a microfiber cloth-covered sponge.  Microfibre cloths are designed to pick up dirt, bacteria and food bits more efficiently and without the use of detergent and then release them all once rinsed in warm water.  We use no detergent in our kitchen accept a mild dish washing detergent.  In theory, these microfiber covered sponges should stay cleaner than their regular sponge counterparts.  We also wash our microfiber sponges and cloths every Saturday on a 60 degree wash.  We tested on a Friday. This meant the toilet should have been fairly clean from the morning chores and the cloth was due a wash the next day.

To be honest, it wouldn’t have surprised me if the dish cloth harboured more bacteria than the loo.  The loo looked cleaner and smelt cleaner.  These were the results after four days of growth situated in the dark above the tumble dryer in the bathroom:


As you can see, the control has no growth in it at all, whilst the dish cloth has a few small colonies growing.  The loo has (thank goodness) got many, many more cultures growing in it than the dish cloth.  Of course the true test will be on day seven, but can I just say how happy I am right now that I am not cleaning dishes with something that is dirtier than our loo!

We left the petri dishes in their warm, dark quarters until they had been incubating a week (which was how long we had decided to keep this experiment going for).  Would the results still show the same as at four days?  Here they are, after one week:


There doesn’t seem to be a lot of difference between the two after eight days incubation, which may mean that my dish cloth is as dirty as my toilet.  However, what the photo doesn’t show is that the bacteria cultures from the toilet look different to the cultures from the dishcloth.

Will this change anything in our house?  Well, I guess I’m content with how clean I keep the loo these days, and to be honest I wouldn’t want to bleach it more than two times a day.  The dish cloth is another matter.  Even though the microfiber cloths have a reputation for not harbouring bacteria, mine obviously do.  In fact, they harbour more of the little critters than I would ideally like.  I am picturing us washing up and smearing all those bacteria over plates and cups.  Urrrk!

After some deliberation, I have decided to chuck the dish cloths in a wash each day, along with tea towels and floor towels and hand towels….  I wouldn’t consider myself pedantic about germs and the like as I’m not convinced too sterile an environment is terrible healthy to grow up in.  We need to expose our children to germs to strengthen their immune system.  And I’m pretty happy with our immune systems in general.  Only one child has been on antibiotics (A5 once for a chest infection) and two have been given them prophylactically to prevent an infection in nasty, deep cuts.  Three courses of antibiotics is fairly good for a family of seven over twelve years.  That said, the idea of items in the house whose duty it is to clean being filled with bacteria creeps me out a bit.  To chuck on one extra wash a day is nothing and at least when we are washing up in future we can be sure the bacteria load is being kept to an absolute minimum and that the sponge is actually helping to clean rather than dirty the dishes!

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  1. Absolutely fascinating stuff. I love how all your experiments link up. (I read somewhere recently that unschooling is all about the connections.) We bung most dishes in the dishwasher but I’m off now to boil my surface wiping cloths!
    My mum always used to say that she was much laxer about cleanliness than her sister and her kids (us) were always far healthier. 😉

    1. With five children and seven animals it would do my head in to be pedantically clean! That said, I’m definitely being a little more careful with my dish cloths!

  2. Now you’ve done it! You’ve forced me to go clean the house. Top to bottom. Inside to out. HA!
    What a neat experiment. I think we should do that around here. Folks would probably be surprised. I have been trying to convince my daughters not to set their purses on anything but the floor of the house. I have heard that purses are the worst for germs. We may have to try your experiment to find out.
    We use our dishcloths for one day and toss them in the wash. Now I am wondering if I should use a couple each day. Hmm. Another experiment.
    Thanks for the great ideas and information. Have a lovely day, Claire.

    1. Is a purse a hand bag? We call where you put money purses. I’d never thought of hand bags harbouring germs but you are probably right. They go everywhere with us and are often placed on the floor.
      Happy cleaning!

      1. Yes, our purse is your handbag. Now that I think about it, I am not too sure I want to know what is on the bottom. Scary thought!

  3. Fascinating experiment, Claire. I hadn’t thought about this issue (dish cloth vs toilet) until I’ve read your post. Hmm, I’ll have to review my cleaning routine as well!

    1. Thanks Hwee! I was a bit grossed out when I read the report, but I could so see how it could be true. I think we are all more diligent with our loos than dish cloth, especially when we have little ones toilet training.

  4. Hi Claire,
    lol. Love your science!! We use disposable towels in our kitchen but what an eye opener!! Thanks too for linking up with us at Finishing Strong each week. I look forward to seeing your school each week..

  5. I love the experiment! We use dish rags and grab a new one each day. If we have an especially dirty day we change mid-day as well. They get tossed in the washer as there is always laundry to run in a family of 10.

    I’m really enjoying reading how project based learning works at your house (and about the ups and downs you’re learning along the way).

  6. Haha this was a great post! I love science that has a bit of the ick factor 🙂 and is linked with real life. Having said that, ignorance is bliss and I will not be replicating! I would be curious as to how the bacteria experiment would turn out at the end of a one day use for a cloth, rather than a week.

    1. It really does have an ikk factor doesn’t it? You know I washed my dish cloth and within hours the next day it still had that dishcloth smell to it. I wonder…..

  7. I feel the need to have a go at this experiment. When I sliced my finger open last week my stupid gut reaction was to grab the first thing to hand to wrap it up in whilst I applied pressure and ran to my husband for help. You may know from my blog that I ended up in A&E two days later with an infection ( prob tetanus apparently – yummy). I am convinced that it was the mistake of using the dishcloth that caused the infection and that’s why I am now curious to prove my theory correct with this experiment:)

    I love your blog – it’s so detailed:) thank you for linking up to this weeks #homeedlinkup

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