No one likes being sick, and with a close family, sharing is not limited to just beneficial gifts. Microbials like bacteria and viruses get passed between people as one kid gives their cold to the next! During “flu season,” it is important to have many ways to fight back against illnesses. We clean and disinfect counters and floors, doorknobs and faucet handles, but with so many airborne pathogens, what about the air we breathe? What if we could also clean and disinfect the air in our homes?

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Essential oils are a popular way to add a subtle all-natural fragrance to your house. They are easy to use because essential oils are volatile by nature, which means they evaporate and disperse easily in the air. Since I already use an ultrasonic diffuser as an “air freshener” for its natural aromatic properties, I wondered if could I use it to purify the room air as well? Several common herbs are well know for their antibacterial, antiviral and antifungal properties. But would these same bactericide, fungicide and virucidal compounds be present and effective in the essential oil when dispersed in the air as apposed to having direct contact with a surface? Numerous people have expressed their broadly differing opinions on this topic on an even wider variety of websites. Yet opinions aside, I wondered what scientific research was available on the topic?

While there are many professional scientific articles published, helping you discover the best in antimicrobial essential oils required a bit of digging. I was looking for studies that tested whole essential oils, not just one of the natural chemical components, and which researched the vapor phase of essential oils not just their topical liquid application. Of particular interest was a resent study which concluded, “These results suggest that all the tested essential oils might be used as broad-spectrum antimicrobial agents for decontaminating an indoor environment.” (1) That’s a pretty impressive statement! So just what were the antimicrobial essential oils tested by this 2017 study? This report used six common essential oils: oregano, thyme, clove, lavender, clary sage, and western red cedar. The effectiveness of these essential oils were tested against 9 bacteria and 5 fungi. Included were common pathogens like E. coli, Salmonella, Listeria and Staphylococcus.

As it turns out, essential oils act differently when used in their liquid form (like topically) verses when used in their vapor phase (diffused in the air.) Some oils are even considered to be stronger antifungals in the vapor phase than when used topically! Their test method employed evaporation and the possible explanation they gave for this increased fungicidal property would require the use of a waterless nebulizing diffuser to recreate the same effect.

Another study of diffusion by evaporation compared 14 essential oils against 5 strains of respiratory tract pathogens and a control bacteria. These pathogens included 3 strains of the bacteria which causes Strep Throat (including a penicillin resistant form) as well as the bacteria responsible for Staph infections. E. coli was used as the control. While “All of the essential oils examined exhibited antibacterial activity,” (2) the essential oils of cinnamon and thyme proved most effective against all six strains at the lowest concentration of oil defused per unit of air. Please note that the cinnamon essential oil used in this study was true cinnamon not cassia essential oil. Lemon grass was also quite effective against all the respiratory pathogens, but showed only limited activity against E. coli. Other oils that showed moderate activity against the respiratory tract microorganisms were perilla, peppermint, tea tree, coriander and both spike and true lavender. These were followed at slightly higher dose by rosemary and eucalyptus. Keep in mind that the bacteria in these tests were only exposed to the vapor phase or gaseous essential oils diffused in the air!

Another interesting study conducted in England tested a commercial fragrance diffuser in an office setting with lemon grass and germanium oils, as well as a commercial blend of these oils. I tried to find additional technical information about the diffuser used in the study, but all my searches came up empty. From the research paper’s description, I would surmise it was a nebulizing diffuser. Of particular interest was the researcher’s observation of an 89% deduction in the room’s airborne bacteria after 15 hours of diffusing at a constant rate with the blended oil. They concluded that “EO [Essential Oil] vapours inhibited growth of antibiotic-sensitive and -resistant bacteria in vitro and reduced surface and airborne levels of bacteria.” (3) Quite an impressive statement given that the pathogens tested in the lab aspect of this study included MRSA, VRE and C. difficile! The authors’ noted further that the “Results suggest that EO vapours, particularly [brand name removed], could be used as a method of air disinfection.” (3)

The following study researched yet another aspect of essential oil diffusion. The effect of essential oil particles in the air we breathe on common respiratory tract pathogens. Using ethanol vapor as a control, they tested the essential oils of thyme, clove, cinnamon bark, scots pine, peppermint, eucalyptus and citronella against 6 bacteria strains including Strep. They found that different antimicrobial essential oils proved most effective on different pathogens. So knowing which pathogen is present would help in selecting the most effective essential oil in a given situation. Yet when considering the overall effectiveness of each essential oil on all of the bacteria studied as a whole, they concluded, “The EO [essential oil] of thyme, clove and cinnamon bark may provide promising antibacterial activity against respiratory tract pathogens either in liquid medium or in vapor phase.” (4)

But what about viruses you ask? Researchers in Australia studied the effect of defused tea tree oil on killing airborne influenza viruses. After five minutes of exposure to the tea tree oil containing air, the treatment chamber contained an almost 97% reduction in the concentration of live viruses when compared to the five minute sampling of the control chamber! No live viruses were detected in the treatment chamber during the three remaining samplings at 15, 30 and 60 minutes. The authors concluded that “essential oils could be successfully utilized as effective disinfectant against of broad range of microorganisms.” (5)

Taken together, these scientific studies point to exciting natural possibilities and a new simple way for using a diffuser to clean and disinfect your family’s home! Ready to start up your diffuser right away? Before you jump to it, stop and think about who else shares your home. Antimicrobial essential oils that are great for killing pathogens may not be the best for your furry housemates. Pet lovers should be aware of the tolerance differences between humans and animals in regards to essential oils.

Cat are very sensitive to polyphenolic compounds so those families with house cats should use cation with polyphenolic containing essential oils like cinnamon, tea tree, thyme, birch, wintergreen, clove and oregano. These compounds are said to interfere with the feline liver’s ability to detoxify. Recommendations range from limiting the cat’s access to the room when defusing to total avoidance of these oils in households with cats. So if you have a pet house cat, further research on the topic is definitely warranted.

For dog lovers, the list is a little more vague with complaints that run the entire spectrum from allergies and skin sensitivities to interference with body processes. The list of essential oils to avoid also differs depending on the source, but anise, clove, garlic, horseradish, juniper, thyme, wintergreen and yarrow are commonly listed. I have also seen cinnamon and tea tree on these lists, yet on the other hand I know a very knowledgeable individual with indoor dogs who uses tea tree frequently without issue. So again, if you have house pets, it’s wise to do your own additional research. Keep in mind as well, some oils are best used with care if there are young children in the home.

One more consideration, in order to recreate the ratio of essential oil vapor per unit of air found effective in these studies you need to know the output of your diffuser. Unfortunately, I could not find this important piece of data on any commercially available diffuser I studied. Simply put, using a diffuser to disinfect is dose dependent, the success of the endeavor requires more than simply choosing an antimicrobial essential oil or combination of oils. There are a few other considerations to heed. The type of diffuser you use (evaporation, waterless nebulizer, or ultrasonic), the length of time it runs, the frequency of use, (daily, weekly, monthly) the setting (continuous or intermediate), and even the amount of essential oil added to the diffuser all effect the outcome. Other considerations are things like the size of the room, architectural features like vaulted ceilings and air flow from ceiling fans and open doors or windows. All of these things can effect how much of the antimicrobial essential oil is ultimately defused in the room’s air. But don’t despair, simple considerations like remembering to consistently use the diffuser, running more than one diffuser in a large room, or alternating which rooms have the diffusers on different days to give better coverage to the whole house can go a long way toward helping you reach your goal. After all you are trying to improve the health of your home, not sterilize a bio-hazard containment zone!

Now we get to the creative part of using the aforementioned antimicrobial essential oils to design aromas that fit your personal taste and needs. You can choose to diffuse a single oil or blend you own mixture. The combination of oregano, lavender and thyme is one I particularly enjoy as all three are documented as effective antimicrobial essential oils in these scientific studies. It’s great for that “what do I do now” moment when you get the after-visiting phone call from apologetic relatives to say they just came down the flu! But don’t limit yourself to only using combinations from these oils. Adding another oil to your antimicrobial essential oil creations can offer a multitude of refreshing combinations. Consider the welcoming aroma of an English Country Garden that can be made by adding sage to rosemary and thyme. Or wintertime get togethers made cozier by the warm and soothing combination of cinnamon, cloves and orange. Want a fresh revitalizing aroma for the summer, then try the cleansing fragrance of tea tree, eucalyptus and lemon. Need an antimicrobial aroma for that special event? Use your creativity, a willingness to try and add some plain old trial and error experimentation to find that perfect backdrop for the kids play-date or that neighborhood committee meeting!

Please keep in mind that the quality of your oils is reflected in both their effectiveness as an antimicrobial and in the aroma they produce. I have two bottles of tea tree essential oil. One is a well know but cheaper quality brand while the other brand is know for its purity standards. Their aromas are quite different. In fact, without reading the label, you would not know they were suppose to be from the same plant!

There are a lot of essential oil brands out available, some good and some not so good. I personally use Edens Garden brand essential oils. I appreciate their broad selection of harder to find oils, the larger sizes they offer (1oz and 4oz!) and their commitment to both quality and cost effectiveness.
Eden’s Garden has an impressive quality ranking coming alongside (and in some cases superior to) well known multi-level marketing brands such as DoTerra and Young Living, but without the high price tag associated with these MLM companies. Eden’s Garden is an American based business with a great ethic and sustainable business practice. They are also a female-owned family business. While several well known brands only randomly test their batches and have even failed third-party testing, Edens Garden conducts third party testing on EVERY BATCH of essential oils to insure a great product! Their packaging in well done, but in the unfortunate event of broken bottles, their customer service has provided me with prompt and courteous replacement. (No, I am not connected with Eden’s Garden. Just a very happy customer pleased with a high quality product offered at a reasonable price.)

Want to learn more about the amazing herbs from which some of these essential oils originate? Check out our blog post on the history and growing of thyme, oregano and rosemary.  Interested in including these antimicrobial herbs in your cooking, give our Lemon-Herb Roasted Red Potatoes with a Dutch Oven Variation a try! Just one more way of helping you discover a few of the many opportunities to incorporate the benefits our plant-friends in our lives!

Keep on learning, the Homesteading Hen

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Notes:

1. Puškárová, A., Bučková, M., Kraková, L. et al. “The antibacterial and antifungal activity of six essential oils and their cyto/genotoxicity to human HEL 12469 cells.” Scientific Reports 7 (2017): 8211- https://doi.org/10.1038/s41598-017-08673-9

2. Inouye, Shigeharu, Takizawa, Toshio, and Yamaguchi, Hideyo. “Antibacterial activity of essential oils and their major constituents against respiratory tract pathogens by gaseous contact.” Journal of Antimicrobial Chemotherapy, 47,5 (May 2001): 565–573, https://doi.org/10.1093/jac/47.5.565

3. Doran, A L et al. “Vapour-phase activities of essential oils against antibiotic sensitive and resistant bacteria including MRSA.” Letters in applied microbiology vol. 48,4 (2009): 387-92. https://doi.org/10.1111/j.1472-765X.2009.02552.x

4. Ács, K., Balázs, V.L., Kocsis, B. et al. “Antibacterial activity evaluation of selected essential oils in liquid and vapor phase on respiratory tract pathogens.” BMC Complementary Alternative Medicine 18 (2018): 227- https://doi.org/10.1186/s12906-018-2291-9

5. Pyankov, Oleg V., et al. “Inactivation of Airborne Influenza Virus by Tea Tree and Eucalyptus Oils.” Aerosol Science and Technology, 46,12 (2012): 1295-1302. https://doi.org/10.1080/02786826.2012.708948