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My daughter, Annika, wanted to do a science fair project that focused on medicines that come from plants.

First of all, my heart nearly exploded with happiness to hear about her interest in the topic that was my first passion in life – medicinal plants.  I was the kid who would take out books from the library on the subject and take notes.  I was also the kid at summer camp who would mash up leaves to treat the other kids’ bee stings and bug bites.  I have always been fascinated by plants, and aspired to be an herbalist or naturopath when I grew up.  I even interned one summer for an herbalist in high school to learn about what that career was like.

But, seeing as it is winter, and the science fair is in Mid-March, our options for harvesting plants were few.  Then I realized we had some potent plant extracts in the house – essential oils!

Now, I have heard people raving about the magical amazing wonderful properties of essential oils to cure every single ailment that ever thought about ailing people.  And I have heard the skepticism about essential oils and how they could sometimes be harmful.  I fall somewhere in the middle: I think some plant essential oils do contain chemical compounds that have the potential to benefit human health in some way.  I don’t think they are a magical cure-all that will remove the need for conventional medicine, but I do think they have their place.  For example, we created a homemade “Vick’s Vapo Rub” alternative, using mostly melted coconut oil, a dash of olive oil, and a few drops of both mint and eucalyptus essential oils.  This salve helps my kids sleep through the night when they are congested.

I couldn’t think of an experiment that would test some hypothesis about the general therapeutic benefits of essential oils – I needed something we could test in a concrete way.  So I settled on the issue of fighting bacteria.

I ordered a kit on amazon: 10 sterile plates all ready to go with LB media (like jello designed to grow bacteria.)   Click here to see what we bought.

We designed an experiment to see which of the essential oils we had in our home would kill or slow the growth of bacteria on these plates.  Keep in mind that this experiment was designed for and executed by a 3rd grader.  😉

Here was our setup:


Annika and I made garlic oil by crushing a clove of garlic into a little warm avocado oil.  I have used this remedy to fight off ear infections in my kids, so I thought it would be prudent to include it in this experiment.


We needed a source of bacteria.  Then JJ (my 2-year-old) pooped in his diaper, and a lightbulb went off.

I made my husband collect a sample of JJ’s poop (because I didn’t want to touch it) and dilute it in a spray bottle.  Super gross.

antibacterial essential oil experiment investigation test

We sprayed each plate with one spray of this horrible concoction.

Then, each plate was treated with either plain avocado oil (the control) or an essential oil.  I thought it would be helpful to add food coloring to the essential oil so we could see where we put it on each plate, but that was a terrible idea because food coloring is not oil-soluble.  So if you do this experiment at home, don’t bother with food coloring.

We put a little essential oil in a separate plastic spoon for each plate, and then transferred as close to 1 drop as possible into the center of the plate (or as close to the center as Annika could make it.)  Keep in mind, aside from handling the poop, Annika was the one carrying out this experiment.

antibacterial essential oil experiment investigation test

antibacterial essential oil experiment investigation test

Here is what we had once all the medicines were applied:

We took the 10 plates, stacked them up, wrapped them in plastic wrap (so they wouldn’t dry out) and put them inside a little cardboard box.

We put the box on a heat mat designed for heating seedlings, to warm them just enough to simulate something close to body temperature.  Bacteria grow much faster at this temperature.


The next day, our power went out, so the bacteria were ignored for a total of 4 days before we observed them.

Here is what we saw when we unwrapped the plates:

antibacterial essential oil experiment investigation test

Our controls worked beautifully – the control with no essential oil grew nice round bacteria colonies.  The control with hydrogen peroxide grew absolutely nothing.  These controls gave us a good point of comparison for the other plates.

It might be hard to tell from the picture, but only one of the essential oils produced little to no growth: clove oil.  Tea tree came in second, and oregano and basil definitely inhibited growth somewhat – there were areas where nothing was growing and areas where tiny bacteria colonies were forming (much smaller than the colonies on the control plate.)  Eucalyptus oil was a cool plate because you could see exactly where the eucalyptus oil had been …. but there were still tiny colonies trying to grow even there, and large colonies around that area.  The frankincense plate contained very little bacteria but something cloudy was growing …. yeast?  Fungus?  I don’t know, but it was gross.

The grossest plate by far was garlic oil – several different species of EW were growing on that plate.  Hand sanitizer was a dismal failure …. it looked similar to, if not worse than, the control plate.  It did nothing to kill germs.  Maybe we should be spraying hydrogen peroxide on our hands instead of hand sanitizer.  I have never been a fan of hand sanitizer, and now I am even more opposed to it.  It sure didn’t stand up against poop germs!

My conclusions:

  1. Clove is a potent anti-microbial agent!
  2. Garlic oil is an old wives tale … very little germ fighting powers, and might even introduce new germs (or molds…) to the system.
  3. Tea tree, basil, oregano, and eucalyptus may slow or inhibit the growth of bacteria.
  4. Hand sanitizer is useless against poop germs.
  5. Hydrogen peroxide kills everything.
  6. Frankincense might be worth investigating further, as the results were tough to interpret.
  7. From now on, I will fight germs with clove, tea tree, oregano, eucalyptus, and maybe basil oil.  (When/if antibiotics are not necessary or ineffective.)

I was really surprised by the results, and from now on, when my kids have an ear infection, I won’t be using garlic oil to treat it.  Ew.  I might try a diluted clove oil though…

Today, I made a batch of chai tea (heavy on the cloves) and fed it to my kids and myself.  Can’t hurt, right?  😉



Please be careful when using essential oils on humans or pets!!!  Some essential oils are not safe for pets or children, and some will cause contact burns if not diluted properly.  I am not a doctor and cannot offer medical advice!  This experiment was done on plates, not on people …. so these results might not be applicable to living creatures.  Be super careful when making your own medicines, and be sure to dilute things!  Better safe than sorry, right?

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