[Sciences/Junk Sciences] Essential Oils: The good, the bad and the ugly science behind some claims

Essential Oils (EOs for simplicity). These little bottles are almost everywhere. Advertised as “natural”, “pure”. Some even are trying to sell them as the next big fad. as the next “miracle cures all” remedy.

Everybody swears by EOs, giving them some curative properties despite the lack of evidence backing such claims. Their therapeutic activity is far from being demonstrated, but their ability to siphon wallets and fill bank accounts of those selling them is as efficient as  the Bernouilli’s principle.

The problem with EOs is to sort the good, the bad and the ugly science behind them.

@MommyPhD recently pointed this out in a nice chart taken from a company making a living on EO.

What I can tell, as the pharmacologist that I am, I was not only perplexed but mind-blown by this chart. It was not a nice mind-blowing effect. It was more like a trigger that turned into a “ballistic mode”.

Just see by yourself the chart below:

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What is wrong? Well, all the claims from the original infographic (left) are wrong! It just simply no sense if you have any basic in pharmacokinetics. Its time for the BBB scientist to deflect such woo with some science deflector shields.

First, in order to understand EOs, you have to understand their origin. To understand their origins, you have to have some basic understanding of pharmacognosy.

Pharmacognosy and EOs:

Pharmacognosy is the science that studies the chemical and biological properties of substances produced by plants and fungi. They are seasoned experts in botany, plant biology and analytical chemistry. Their main interest is to extract chemicals from different part of the plant (stem, sap, roots, leaves, flowers, fruit….), identify the substances present in such extract and identify their possible biological properties (this is often linked with ethnopharmacology, in which scientists are trying to identify the potential of some medicinal plants with their use from healers and shamans).

Plants and fungi synthesize two major classes of molecules: those involved in the primary metabolism and those involved in secondary metabolism.

Primary metabolism mostly aimed to ensure growth plant and reproduction. You can consider it as the core chemical plant. These are chemicals important for the plant function.

The second metabolism is on its own very interesting. At first, these compounds have no role in plant growth and therefore may appear useless. Indeed compounds produced from secondary metabolism are very important for the plant because these are essential for its survival. Plants evolved to have limited mobility and therefore are easy target for predators. But what plants traded out for limited mobility have indeed traded in one of the most sophisticated chemical warfare. Plants have evolutionary developed one of the most advanced and versatile chemical warfare aimed to control and deter any dangerous entities that may compete for limited resources (water, minerals, oxygen, light, CO2…).

Here are some examples of chemicals synthesized by plants secondary metabolism: Caffeine, atropine, cocaine, morphine, tetrahydrocannabinol, strychnine, nicotine, digoxin, ouabain, terpenes, cyanide, colchicine, vinblastine, paclitaxel, acetylsalicylic acid, phalloidin, forskolin, turmeric acid…….these are all products from the secondary metabolism. Many of them sounds like “poisons” and they are rightly called poisons because they can kill you at the right dose. But if you use these compounds at the right dose, these compounds can also be used to treat cancer, heart failure, glaucoma……..considering the dose makes the poison.

EOs are a particular class of chemicals, because they harbor particular chemical features. They are volatile (they belong to the superclass of volatile organic compounds or VOCs), lipophilic (soluble in fat and oils) and are odorant (this is why we can smell them). They are also capable of some biological activity.

These EOs have to be extracted from the plants via the use of organic solvent. One of the most common solvent is ethyl alcohol or ethanol (CH2OH), that is convenient organic solvent. Ethanol can help dissolve both lipophilic and hydrophilic substances. It is also has a low evaporation temperature (78ºC), allowing it to dissipate fast once on skin contact.
Another property of these compounds contained in EOs is their ability to become volatile. We can refer these compounds as volatile organic compounds (VOCs). This is why we use them as fragrance. Because they are volatile, these compounds are spread in the air and can be caught by our olfactory receptor neurons (ORNs), making what we refer a smell a smell. Smells are very powerful stimuli, even for humans. This is why we are all fond of “eau de toilette”, “eau de parfum” and all these molecular cues that can turn our reptilian brain upside-down.

EOs are very diverse by their origin and their composition. For the simplicity of this article, I will focus on the major source of EOs by their production: Citrus sirensis (sweet orange) and Mentha arvensis (mint) EOs. These are the two most prevalent sources of EOs worldwide.

Two studies that I have found listed the EO composition from these two plants.  C. sirens is  has about 50 different compounds identified, mostly classified as terpenes. M. arvensis  have about 30-40 compounds including terpenes and other organic compounds (http://www.ifrj.upm.edu.my/18%20(04)%202011/(10)IFRJ-2011-062.pdf and http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.927.8806&rep=rep1&type=pdf)

EO composition vary between cultivars, between crops, between extraction procedures. …..It means that EO by nature are anything but “pure”. EOs are therefore impure because you have a mixture of different compounds at different concentrations. It also means  that such EOs are setting the perfect storm for some drug interactions and some toxicity due to photo activation (some terpenes like limonene are know to become phototoxic following exposure to light)  or induction of an allergic reaction.

Pharmacokinetics and EOs:

In this second part, we will refute the claim brought about the penetration and tissue targeting mentioned in the infographic. The infographic have it wrong at so many different levels but two are striking: firstly, the sequence of events followed the extent of these events.

In order to understand the rebuttal, we have to understand some basic aspect of pharmacokinetics (PK). PK is the science that will tell you the fate of a chemical in your body. It will tell you how it is absorbed, how much reach the bloodstream and the tissue, how it gets detoxified and finally how it gets eliminated.
PK focuses on the fate of drugs inside our body, whereas toxicokinetics (TK) focuses on the fate of poisons and toxins inside our body.

Both follow the ADME acronym: Absorption (tegumentary/skin, intestinal/gut….), Distribution (bloodstream, tissues and brain), Metabolism (“detoxification” via chemical transformation and inactivation by the liver) and Elimination (via the liver and kidneys).

This is where the infographic has it completely wrong. It makesthe assumption that the EOs enter the brain, then the bloodstream and finally cells is just what I call “bullshit” and simply a reflection of a sheer ignorance of human anatomy and physiology. I dragged a small sketch to described the EOs ADME profile.

EssentialOilFirst, EOs have to pass the skin (or gut) barrier and diffuse all the way through the bloodstream. This operate through a passive gradient that result in the progressive loss of EOs compounds during the diffusion (depicted by the yellow arrow) into the bloodstream. This phenomenon is called “bioavailability” and investigate how much of a compound can reach the bloodstream following an administration route that is not obtained via direct injection into the bloodstream (intravenous or intra-arterial).

At the end of the day, this is the appropriate order of sequence: skin->bloodstream->brain (if you are lucky enough).

The amount of compounds contained in the EOs reaching the blood circulation remains unclear and poorly understood. But we can use some analogies with known chemicals. We will discuss the case of hydrocortisone (a topical steroid) and nicotine (a known compound capable to cross the BBB and act on the central nervous system).

Hydrocortisone is commonly used by practitioners to treat skin rashes and other irritations with a cream. The good thing about it is that such cream act topically. A thesis has documented previous studies that estimate about less than 5% of the amount of hydrocortisone applied to the skin was able to get a full ride into the kidneys (https://www.unispital-basel.ch/fileadmin/unispitalbaselch/Bereiche/Querschnittsfunktionen/Spital-Pharmazie/Diss_Pellanda.pdf). It is also telling you that a topical administration is probably not the best option for administration of a drug.

Now, there are other cases of topical administration that result in brain delivery. This is the case for nicotine and nicotine patches. These delivery systems are good in giving a good bioavailability, but yet these compounds will take some time to reach the brain. Considering the tmax (time by which a compound reaches a maximum plasma concentration), such delivery systems can only deliver nicotine with a tmax of 5-6 hours following patch application (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1364642/?page=4). You can understand that the probability of compounds contained in EOs to reach the brain within 30 seconds is impossible, unless you perforate the skull and perform an “intraventricular injection”. This is a very invasive procedure requiring a brain perforation and the insertion of a canule deep inside the brain.

Now we can argue that some drugs can reach the brain within minutes following injection. This is true for anesthetics like propofol. However propofol administration route and chemical properties are very different from EOs: they are injected via IV infusion and propofol penetration across the blood-brain barrier (BBB) is known and documented. Yet, it still takes about 4 mins for a IV infusion of propofol to achieve tmax , making the alleged claims of 22 seconds in the infographic completely bogus (https://www.fda.gov/ohrms/dockets/ac/08/briefing/2008-4354b1-01-FDA.pdf).

Even if your compounds can diffuse the skin barrier at the speed of light (100% absorption and bioavailibity) and have no metabolism (0% loss in EO compounds), you still have to demonstrate that such compounds can cross the blood-brain barrier (BBB). The BBB  blocks about 95% of chemical compounds known by humans. Therefore it is very unlikely that all these EO compounds magically fall within the 5% range.

In addition, analyzing the fate of every single chemical compound present in one EO can be an analytical nightmare even for the most seasoned analytical chemist. @SciBabe can explain you that in more details.

In conclusion, the ability of EOs to exert their biological activity beyond their skin application is simply “dead in water” and subsequently the claims posted in the infographic.

EOs and their “therapeutic claims”: the FDA warning letters
EOs may smell good but they have no scientific basis to support their claims of therapeutic use as depicted on their website. This is why the FDA has decided to enforce its authority via warning letters to two companies.

In 2014, the Food and Drug Administration (FDA) sent two warning letters to Young Living (https://www.fda.gov/iceci/enforcementactions/warningletters/2014/ucm416023.htm) and DoTerra (https://www.fda.gov/iceci/enforcementactions/warningletters/2014/ucm415809.htm) noticing them of the violation of the Food, Drug and Cosmetic Act by advertising therapeutic claims that have not been asserted. Unless you file an application in which you document with a great care the safety and the efficacy of a therapeutic agent, you have no rights to make a claim that compound X will prevent or cure cancer or other illnesses. What was true for these two companies also applies for any companies selling EOs.

Do not use EOs to treat or cure any illnesses because their therapeutic activity have not been proven by scientific methods. Worse, if misused these EOs can become dangerous poisons if swallowed  (http://www.poison.org/articles/2014-jun/essential-oils). You have been warned.

In conclusion,  EOs make great scents and fragrances to make your house smell nicely. But that should be their only application. Use them as personal fragrances with extreme precautions and avoid their swallowing and use as medicines.