What’s in your bottle? The Answer is not as simple as you’d think: The Adulteration, Degradation, Contamination and Misrepresentation of Essential Oils. Plus an Idea of How to Make Things Better
You may notice that the style of this article is slightly different than you’re used to seeing on Marvy Moms. What follows is the required research paper that is part of my aromatherapy certification at Aromahead Institute. Andrea Butje graciously provided comments on my paper that are included in this revised version you see here on Marvy Moms. As I was getting ready to press “Publish” on this article, I received notification that I am now officially a Certified Aromatherapist! I will be sure to share my experience of 235 hours of coursework as well as writing the paper you see here and the 20 required case studies. I may even share a few recipes that I’ve created along the way!
Essential oils are concentrated fat soluble and volatile aromatic substances that are coaxed from the leaves, stems, flowers, wood, and/or roots of plants through distillation. They are used in aromatherapy to evoke a desired effect such as reducing inflammation, muscle spasms, depression, anxiety, or pain, or increasing self confidence, sense of calm, or the immune system’s ability to fight infection and repair the body.
Dr. Robert Pappas makes the distinction that essential oils are “products produced by steam or hydro-distillation (with the exception of cold pressed citrus oils).”1 Absolutes, Concretes, Florasols, and CO2 extracts are not produced by these means and therefore are not essential oils. For the purpose of simplicity within this article, all of the above will be referred to as “essential oils” and the term “extraction” may be used to mean any method by which these aromatic substances are coaxed from plant material.
Pharmaceutical drugs are synthetic substances (often based on chemical components found in plants) that are manufactured to exact specifications in order to produce a predictable response in a living organism. Pharmaceuticals are often designed to work on a specific symptom or group of symptoms (disorder or disease). While they may do this to a great degree in many people, they rarely do so without significant side effects ranging from mild things such as dry mouth or drowsiness all the way up to psychotic episodes, neurological symptoms or in the most extreme case: death.
Nature Resists Any Attempt to Be Controlled
Considering that unadulterated essential oils are natural substances that have not been prepared in a laboratory, there is no standardization of what chemical components are contained in a particular oil. Science has yet to find a way to completely “control” nature. Although science has managed to create genetically modified organisms (GMO), they are not able to standardized plant material to the degree of complexity found in nature.
Plants are subjected to the many variables of nature such as climate, weather, insects, soil conditions, weeds, etc. On top of that is interference by humans to control these variables: watering plants, pesticides, fertilizers, and other various methods. Each variable changes the final chemical composition of a plant.
The process of extracting an essential oil from the plant can further change the chemical composition of an essential oil. In steam distillation, the temperature and length of the distillation has an effect. Other variables include solvents used, extraction type, time of the harvest of the plant, length of time between harvest and extraction, and design and cleanliness of the still.
What’s in the Bottle
Once the essential oil is extracted from the plant, there are additional ways in which it can become altered in some way:
- Degradation (poor storage conditions or prolonged storage2)
- Dilution with carrier oil
- Mislabeling (intentional or not)
- Dilution with other chemically similar essential oils
- A reconstituted oil
- Pure aroma chemical
The British Pharmacopoeia requires that Eucalyptus oils contain a minimum of 70% 1,8-cineole content. When an oil contains less than this after distillation, it is commonly redistilled to increase the percentage of 1,8-cineole. This process of redistillation is called rectification. As the 1,8-cineole content increases, other constituents may decrease or even completely disappear from the final product. This rectification process may satisfy the requirements of the British Pharmacopoeia, however, from an aromatherapist standpoint, the synergistic healing effect of all the constituents from the original distillation will be minimized or compromised.3
Degradation is the natural process of the chemical breakdown of essential oils. This commonly occurs from oxygen, heat and light. The length of time that it takes this process to occur can vary grately based on storage conditions. Some essential oil retailers take great care in storing their essential oils in conditions that reduce exposure to oxygen, heat and light. Some things that help to slow down the process of degradation of essential oils include storing them in:
- dark containers
- glass containers
- a cool environment
- a dark environment
- conditions which minimize exposure to oxygen
At Stillpoint Aromatics, “Each bottle is “nitrogen capped” forming an oxygen barrier, which decreases the oxidation process immensely.”4 Meg Shehad at Gritman Essential Oils said, “We used to put oils in metal, but oils didn’t like that. So, now we have wall to wall glass jugs of oils because the oils are happier.”5
Essential oils can be decanted into smaller bottles as to reduce oxygen exposure during storage.
Recently several companies, who test, discovered an Indian distiller that they had worked with for many years got their oils from other local small distillers and the oils had been stored in plastic. The test results revealed a chemical leached from the plastic and unintentionally adulterated the oil. The chemical from the plastic container was phthalates. They were so glad they tested, as it was impossible to know this any other way (aroma seems just fine).6
Tisserand and Young, define adulteration as “intentional dilution or fabrication” of an essential oil. He goes on to say that essential oils can be adulterated with “odorous or non-odorous substances in order to dilute an essential oil or absolute. Odorous adulterants can include other essential oils, essential oil fractions or residues, synthetic aromachemicals similar to those found in the oil, or aromachemicals not found in the oil. Non-odorous adulterants, or ‘extenders’, include substances such as ethanol, mineral oil, isopropyl myristate, glycols, phthalates, and fixed oils such as rapeseed and cottonseed.”7
Adulteration can happen at any point from distillation/extraction to reaching the end user. Some points along the way can include:
- Co-gathering or codistillation of several varieties (for example: several types of lavender gathered and/or distilled together)
- Distiller may adulterate an oil before selling it to a distributor
- Distributor may adulterate an oil before selling it to a retailer (most likely)
- Retailer may adulterate an oil before selling it to a customer
Dr. Christoph Streicher of Amrita Aromatherapy states that, “If oils are not bought directly from the distiller, there is always the chance of adulteration. EOs are commonly not adulterated by the producers, but by the current trade system which mainly supplies the fragrance, toiletry and personal care industry. That industry is largely not in need of a natural product but in need of a consistent and well-priced product. A trade system for the needs of aromatherapy still needs to establish itself. To go to the source is a necessity for us even though it means importing many different essential oils from many different sources.”8
“It has also been our experience that distillers rarely adulterate. One interesting thing to note is that sometimes distillers misidentify their oils and we have discovered wrong species and wrong chemotypes several times through testing. The species mis-identification has happened more with conifer tree oils than any other oils but we have seen chemotype mistakes happen with a variety of oils over the years.”9
While any essential oil can potentially be adulterated, there are reasons that some are more likely to be adulterated than others:
- High demand that cannot be met by available crop (ie: lavender, esp. Lavandula angustifolia)
- High cost to produce the oil (ie: rose (Rosa damacena), neroli (Citrus aurantium var. amara))
- Potential to increase profit margin
Some essential oils that are commonly adulterated include: 10 11 12
- Bergamot (Citrus bergamia)
- Blue Tansy (Tanacetum annuum)
- Damiana (Turnera diffusa)
- Grapefruit (Citrus paradisi)
- Jasmine absolute (Jasminum grandiflorum)
- Lavender (Lavandula angustifolia)
- Lemon (Citrus limon)
- Lemongrass (Cymbopogon citratus)
- Patchouli (Pogostemom cablin)
- Peppermint (Mentha x piperita)
- Rose (Rosa damacena)
- Rosemary (Rosmarinus officinalis)
- Sandalwood (Santalum album or Santalum paniculatum )
- Ylang-ylang (Cananga odorata)
During three independent interviews of retail essential oil sellers, I was told that the amount of lavender grown around the world in one year could not possibly match the amount of lavender essential oil that is produced and sold in that same year. So where is the rest of the essential oil coming from? According to Tisserand and Young, “Lavandin oil, spike lavender oil, Spanish sage oil, white camphor oil fractions, rectified or acetylated ho oil, acetylated lavandin oil, synthetic linalool or linalyl acetate” are all common adulterants used to stretch the lavender crop to meet demand.13
Testing Essential Oils
Several tests can be conducted to verify the authenticity of an essential oil:
- Organoleptic testing (smell test)
- Physical measures (density, refractive index, and optical rotation)
- Chemical Analysis (GC/MS – Gas Chromatography/Mass Spectrometry)14
All of these tests are pieces of a larger picture that tell whether an essential oil is authentic or fraudulent. Although GC/MS analysis is considered the gold standard for testing an oil it is not without limitations.
The GC/MS report itself is simply a piece of paper and does not “prove” anything about what is in the bottle of essential oil that ends up in the hands of the consumer. Unless you personally follow the oil from the distiller to the GC/MS machine, to the final report in the hands of the customer, there is no way of knowing what happens along the way. In law enforcement this is called the chain of custody. Evidence from a crime scene is bagged up, sealed, and logged. Anyone that touches the evidence has to sign something that they’ve received the evidence and it has to be sealed again before it passes along to the next person or is returned to the evidence room.
Chemists skilled at adulteration can use synthetics to make a GC/MS report look good based on chemical composition. Essential oil retailers can alter the report once it is received. I’ve also heard speculation that the reports themselves can be made to look a certain way by the tester. There are many variables and opportunities for the report or the oil to be altered before it gets into the hands of the customer.
Most companies change the GC/MS report to remove the name of the tester and add their own logo and make the report available as a downloadable PDF on their website. Some companies go so far as to make their GC/MS reports completely electronic. This can be quite helpful for the consumer, as constituents can be listed according to chemical family and in order of highest to lowest percentages. They are also quicker to view on a website and do not require that anything is downloaded to the user’s computer or mobile device. Despite these advantages, there is likely to be some degree of human error in these reports as they are converted from one format to another.
While some companies have GC/MS analysis done of every batch of every essential oil they sell, many do not. The cost for GC/MS analysis ranges anywhere from $100 to $300 or more per test. This is a significant cost for smaller retailers. On her website, Katharine Koeppen, RA, owner of Aromaceuticals states that, “In many cases, batch testing doubles the cost of an essential oil. Some companies get around that by purchasing cheap, lower quality oils from India or China, factoring in the cost of a batch GCMS, and selling the oils for a lot more than they’re worth.”15 Marge Clark, owner of Nature’s Gift says, “if I have been buying from the same artisan distiller for 15 years, and I KNOW he takes as much pride in his product as I do in ours, should I invest in a test of his oil every single year? The cost, as you well know, would be passed on to the end customer.”16 Andrea Butje of Aromahead Institute says, “Testing is a challenge for smaller retailers and especially for oils like citruses where the test can cost more than the oil.”17
In addition to paying for the test, there is the added cost of time to format and publish the reports so that they are available on their website.
Certificate of Analysis
Many times essential oil distributors will provide retailers with a Certificate of Analysis. This document lists results of any tests done on a batch of oil such as organoleptic testing (smell test), physical measures (density, refractive index, and optical rotation), and/or chemical analysis (GC/MS – Gas Chromatography/Mass Spectrometry). There is no standard for a Certificate of Analysis and the type of information provided is decided by the company selling the oil to the retailer.
Retailers that do not send all their oils out for independent GC/MS analysis, likely still have a Certificate of Analysis on file for any oil they sell. Sometimes this information will be made available on their website for customers to download. As with GC/MS reports, there is rarely any distinction as to whether this report came from the distiller (producer), distributor, in-house retailer lab, or independent lab. Even if the consumer and retailer take this report at face value from the distributor, who’s to say that the oil was not altered after the analysis (before getting to the retailer) or that it wasn’t completely fabricated to start with? GC/MS reports and Certificates of Analysis are pieces of paper and are easy enough to alter or fabricate or contain errors at any point in the process of creation.
Small Amount of Oil Used for Testing
Since GC/MS analysis is a snapshot in time of an essential oil, it does not translate that the oil that was tested is the oil that ends up in the hands of the consumer. Even if no adulteration occurs, there can be degradation for reasons stated earlier or contamination before the oil ever reaches the customer.
GC/MS testing can be run with a very small amount of oil. 1 ml out of the 119 240.471 ml in a barrel is all that is needed to run a GC/MS test. This is the amount of blue tansy that I sent to Dr. Robert Pappas to be analyzed in January 2015. The sample I sent was a 10% dilution from a highly reputable company that I will not disclose. Although he ended up not running a GC/MS report on this oil he stated that, “There is no doubt that the essential oil in the dilution is blue tansy oil.” The problem was that there was a color variation that could not be explained. He said that although the bottle was labeled as a 10% dilution that is was more likely closer to a 1% dilution.18
Example of Contamination Not Detected by GC/MS
In 2015 Plant Therapy had water in the bottom of a barrel of Blue Tansy (Tanacetum annuum) that they didn’t realize until customers complained that something wasn’t right. This is a classic example that there can be things in an oil that has been tested, yet the test shows no contamination. If the sample used for GC/MS and other tests was taken from the top of the barrel, there would be no trace of the water at the bottom of the barrel. When I asked Retha Nesmith, aromatherapist at Plant Therapy, about the incident she replied that “The barrels are dark, our Amber bottles are dark, and the tub we use to fill the bottles is not clear. There was no way we could have known. We have since filled an empty clear bottle before we start bottling and let it sit for a few hours. That way we can catch it if it ever happens again.”
Customer Demand for Tests
In January 2015, Dr. Robert Pappas revealed on the Essential Oil University Facebook page that Blue Tansy (Tanacetum annuum) was a commonly adulterated essential oil and offered to do free analysis of any blue tansy oil that was sent to his lab during the month of January.19 Of the 11 publically shared reports, two of the blue tansy oils analyzed were deemed to be fraudulent oils. Although only 18% of the blue tansy was adulterated or misrepresented, this testing set off a chain reaction of consumers sending in their essential oils to be tested and then publicly reporting the results. A Facebook group called “Blue Tansy Analysis” was set up to share results of any oil tested by the consumer. By July 2015, Blue Tansy Analysis had over 5,000 members, 36 confirmed reports of adulterated and/or fraudulent oils and had posted results of GC/MS tests of essential oils from 20 different companies.20
Due to groups like Blue Tansy Analysis, customer demand for GC/MS reports has gotten so strong that companies are feeling pressured to provide them. They are scrambling to have oils tested and/or to post reports that they already have. Customers are scrutinizing the actions of every company. Well-loved companies that have been in business over a decade are being put into question and criticized for their reaction when test results are revealed or questioned.
The truth is that there is no one company that perfectly sources their oils. Many try, but there will always be exceptions. If every oil from every company were independently tested, chances are good that every company will have at least one or a few oils that are adulterated or misrepresented in some way or another.
The customer’s demand for GC/MS testing and perfect customer service have become a sort of modern-day witch hunt. There are plenty of essential oil retailers that are purely interested in profit and are intentionally selling bogus oils, however, there are many well-established as well as new companies that truly have a love of essential oils and their healing power and are committed to providing quality oils to the consumer.
Essential oils can be sold in several different ways:
- Distiller to Distributor (most common and in large quantities)
- Distiller to Retailer
- Distiller to Consumer (rare and in small amounts)
- Retailer to Consumer
- Online Retail
- Retail Shops
- Multi-Level-Marketing (MLM)
Many consumers are originally introduced to the use of essential oils through exposure by a representative of an MLM. The representative is typically a friend or family member or at least a member of the community and a level of trust exists before the oils are ever bought or used. Two of the largest and well known essential oil MLMs are Young Living and dōTERRA. Both of these companies claim to test all of their oils, however, never release the results of those tests publicly.
Due to a long history of these top companies propagating unsafe use of essential oils such as daily ingestion of lemon oil in water and using oils neat (undiluted) on the skin, there is a rift in the essential oil community about the support of these companies. MLM representatives tend to love the company that they buy from and tout them as being the only pure and “therapeutic grade” essential oils available. There is no official grading system of essential oils so the designation of “therapeutic grade” is merely a marketing term that has no industry-wide standards to back it up.
The mention of MLMs is important here because it explains the background and tone for why the current witch hunts are happening today. Faced with accounts of injury from essential oils, many MLM representatives will dismiss them as exaggeration or complete fabrication. The Injury Report 2014 released by Atlantic Institute of Aromatherapy21 met criticism that it was not “scientific” enough because these were personal reports with no scientific rigor involved in the reporting. Although 24 out of the 34 injuries reported were oils from the top two MLMs, essential oil injuries are not restricted to a particular brand. The high amount of injuries from the top two MLMs could be contributed to the unsafe practices circulated throughout the MLM community. Update: The 2015 Injury Report is also now available.
Faced with accounts of injury from essential oils, some representatives will begin to question the information they’ve been taught by their MLM company. Of these, some will leave the company they signed up with and either stop using essential oils altogether or search for another place to buy their oils. Whenever I mention to someone that I use essential oils, they ask me, “Do you sell Young Living?” No. “Do you sell dōTERRA?” Nope. “Then what do you use?”, they ask with a puzzled look on their face. Every person that leaves an MLM must do extensive research if they want to maintain the standard of quality promised by their former company.
People want the quality of essential oils that are promised by the MLM companies. They want a company that:
- Sells pure oils
- Sells “therapeutic grade” essential oils
- Sells essential oils that are safe to ingest casually (a practice not endorsed by the greater aromatherapy community)
- Tests their oils to prove that they are all the things listed above
- Has impeccable customer service
- Has an owner or staff that are knowledgeable about essential oils
Getting back to testing oils, even testing is not always enough:
- Reports must be available for download or upon request
- Reports must be free
- Reports must not increase the price of the final product
Customers want quality, proof of quality, the best customer experience possible, and the lowest possible cost. Some people will see the value in paying more for testing, but many people are looking to find the best quality for the cheapest cost since this is the only way they can afford to buy all the essential oils that they want to have.
People that have been “burned” by their experience with a MLM company (or any other essential oil company) are overly cautious as to who they will trust next. Since coming from a starting point of only being able to trust one company, they tend to be very selective of where to buy their essential oils. Once they’ve selected a company to trust, they will often buy all or most of their oils from one or two companies.
People that use essential oils are huge fans. They love their oils and they love the company(s) they buy from. They tell everyone about their favorite company and share blog posts and sales by their favorite companies. When evidence of a mistake by a non-MLM company is brought to light it can affect the buying behavior of thousands of consumers. Customers band together and demand refunds and write negative reviews. They pool their money and have oils tested. They email and call customer service and insist upon immediate resolution.
This develops a pattern where customers are in attack mode and retailers are in defense mode. Some retailers are gracious and handle these issues with great ease. Others are less graceful and end up further alienating their formerly loyal customer base. Gloves are donned and customer and retailer duke it out and nobody wins.
As we now know, GC/MS tests that end up in the hands of the customer are a piece of paper that show that at some point in time an oil had the constituents listed on the report.
- The oil can become adulterated, degraded, or contaminated after (or while) the report is generated
- The report can be a partial or complete fabrication and may not be for the current batch of oil being sold
Despite these facts, customers want to see the GC/MS reports. Companies that provide them are praised for providing them and are likely to be even further scrutinized if contamination or degradation occurs after the report is generated (especially if further testing shows different results).
A Possible Solution
How can the essential oil industry meet the demand of providing GC/MS analysis results to the consumer in a way that stops the fight between customer and retailer and holds everyone accountable?
Considering that there are several stops for a GC/MS report to make:
- Retailer orders testing
- Lab tests oil
- Test results are sent to retailer
- Test is manipulated to be readable by the consumer (lab name removed, retailer name added, and constituents may be grouped by chemical family)
- Test is made available to the consumer
At that point a customer may order additional testing to verify the test provided by the retailer and then must interpret the results.
What if we could change this process entirely?
- Retailer assigns a batch number to each batch of essential oil to be tested
- Retailer orders testing
- Lab tests oils
- Lab publishes test results of each batch in a central database
- Lab shows numbers for comparison on report of expected ranges for each component alongside the actual values present in an oil
- Retailers can link to the results in the central database for the customer to view and download
This may seem like pie in the sky thinking, but it is entirely possible in today’s online informational world. The Essential Oil Chemical Reference database contains thousands of literature references and GC/MS reports for many essential oils22, however they are not listed for specific batches of oils currently being sold in the marketplace.
Labs could post these results to a central database and retailers could choose to link to the report after they have decided that the oil is fit for sale. This would set up a culture of accountability and trust among distillers, distributors, retailers and consumers as there has never been before. With all this information in one place, there will be a large body of data to get a better sense of the true ranges of components in each oil.
Each batch result should include information such as:
- Date of Distillation
- Farming method
- Plant part used
- Country of origin
- Distillation/Extraction method
- Other significant growing conditions (high altitude, etc…)
- Batch number
- Other tests performed on the oil
Such a database could be a tremendous resource for the field of aromatherapy. Aromatherapists and researchers could make purchasing decisions based upon components of a given oil.
For anyone that cares to compare reports, there would be the ability of the the customer to:
- See who is selling the exact same oils (common distributor or distiller)
- Choose an oil based on therapeutic properties determined by the chemical makeup of the oil
This solution does not solve every problem. Obviously an essential oil could become altered after the report, however, it may make the intentional alteration at any level less likely. It may also help bring the aromatherapy world together rather than rip it apart.
1. Pappas, Robert. ‘The Definition Of An Essential Oil And Why Wikipedia Is Wrong’. Facebook.com. N.p., 2014. Web. 17 July 2015. https://www.facebook.com/notes/essential-oil-university/the-definition-of-an-essential-oil-and-why-wikipedia-is-wrong/10152588925928083
2. Battaglia, Salvatore. The Complete Guide To Aromatherapy. 2nd ed. Brisbane: The International Centre of Holistic Aromatherapy, 2003. Print.
3. Battaglia, Salvatore. The Complete Guide To Aromatherapy. 2nd ed. Brisbane: The International Centre of Holistic Aromatherapy, 2003. Print.
4. Stillpoint Aromatics,. ‘Storage & Shelf Life’. Stillpointaromatics.com. Web. 17 July 2015. http://www.stillpointaromatics.com/storage-quality-shelf-life
5. Carpenter, Emily. ‘Explore Physical, Mental, Emotional And Spiritual Uses Of Essential Oils With Gritman Essential Oils – Marvy Moms’. Marvy Moms. N.p., 2014. Web. 17 July 2015. https://marvymoms.com/gritman-essential-oils/
6. Butje, Andrea. Research Paper Feedback. 2015. email.
7. Tisserand, Robert, and Rodney Young. Essential Oil Safety: A Guide For Health Care Professionals. 2nd ed. Edinburgh: Churchill Livingstone Elsevier, 2015. Print.
8. Carpenter, Emily. ‘Dr. Christoph Streicher Of Amrita Aromatherapy Sheds Light On Ingestion, Adulteration, And Overdose Of Essential Oils *Plus* A Special Offer For Marvy Moms Readers – Marvy Moms’. Marvy Moms. N.p., 2015. Web. 17 July 2015. https://marvymoms.com/amrita-aromatherapy/
9. Butje, Andrea. Research Paper Feedback. 2015. email.
10. Tisserand, Robert, and Rodney Young. Essential Oil Safety: A Guide For Health Care Professionals. 2nd ed. Edinburgh: Churchill Livingstone Elsevier, 2015. Print.
11. Battaglia, Salvatore. The Complete Guide To Aromatherapy. 2nd ed. Brisbane: The International Centre of Holistic Aromatherapy, 2003. Print.
12. Pappas, Robert. ‘Timeline Photos – Essential Oil University | Facebook’. Facebook.com. N.p., 2014. Web. 17 July 2015. https://www.facebook.com/EssentialOilUniversity/photos/a.10150257060058083.379605.82862428082/10152862475193083/
13. Tisserand, Robert, and Rodney Young. Essential Oil Safety: A Guide For Health Care Professionals. 2nd ed. Edinburgh: Churchill Livingstone Elsevier, 2015. Print.
14. Battaglia, Salvatore. The Complete Guide To Aromatherapy. 2nd ed. Brisbane: The International Centre of Holistic Aromatherapy, 2003. Print.
15. Koeppen, RA, Katharine. ‘Aromaceuticals: Why We Don’t Batch Test Our Essential Oils, Essential Oils From Artisan Distillers’. Aromaceuticals.com. Web. 17 July 2015. https://www.aromaceuticals.com/blog/why-we-dont-batch-test-our-essential-oils
16. Carpenter, Emily. ‘The True Gift At Nature’s Gift Aromatherapy Products – Marvy Moms’. Marvy Moms. N.p., 2014. Web. 17 July 2015. https://marvymoms.com/natures-gift/
17. Butje, Andrea. Research Paper Feedback. 2015. email.
18. Pappas, Robert. ‘Be Careful When Buying Oils In Dilution’. Facebook.com. N.p., 2015. Web. 17 July 2015. https://www.facebook.com/notes/essential-oil-university/be-careful-when-buying-oils-in-dilution/10153175245213083
19. Pappas, Robert. ‘Due To The Proliferation Of Adulterated… – Essential Oil University | Facebook’. Facebook.com. N.p., 2015. Web. 17 July 2015. https://www.facebook.com/EssentialOilUniversity/posts/10153110919643083
20. Miller, Kenneth. ‘RESULTS SO FAR’. Facebook. N.p., 2015. Web. 17 July 2015. https://www.facebook.com/groups/764639060290026/permalink/802872229800042/
21. Sheppard-Hanger, Sylla. ‘Injury Report 2014’. Atlantic Institute of Aromatherapy. N.p., 2015. Web. 17 July 2015. http://www.atlanticinstitute.com/injury-report-2014
22. Pappas, Robert. ‘Essential Oil University » Database’. Essential Oil.university. N.p., 2015. Web. 17 July 2015. http://essentialoil.university/database/