The Internal Use of Essential Oils: An exploration

by Jade Shutes

The Internal Use of Essential Oils

by Jade Shutes

Over the years I have found the interest in the internal use of essential oils to be fascinating. While a couple of companies recommend the internal use of essential oils willy nilly without due consideration for safety, the aromatherapy industry at large simply states not to use essential oils internally.  There are few articles within the industry that shed light on what the benefits and safety considerations should be when taking essential oils internally.  Some simply imply that the internal use of essential oils is extremely dangerous or prone to causing harm.  Although I do understand the need for companies to place this on their label due to liability issues. My core interest is for self care.

This year in particular there seems to be quite a bit of interest in taking essential oils internally.  I want to understand why and how we may benefit from a deeper understanding than either camp has offered up to date.

Our inability, due to legal constraints (although I cannot say I actually know of a single law that states this), to recommend the internal use of essential oils in the treatment of a ‘dis-ease’ in another should not, I believe, dictate our ability and need to understand how and why we would want to use essential oils this way to self treat, should we feel confident to do so. In fact, based upon the growing interest and indeed the growing use of essential oils internally, I believe it is becoming imperative that we in the aromatherapy industry develop a better understanding and richer knowledge base regarding the internal use of essential oils.

Although I am not a strong advocate of taking essential oils internally without just cause, I have used essential oils for myself and friends in vaginal and rectal suppositories for specific conditions (e.g. in the treatment of respiratory infections and hemorrhoids), cough syrups, teas and sometimes in a spoonful of honey.  Each year I make up a supply of cough syrup containing herbal and aromatic ingredients. I always use my own essential oil based mouth wash and drink a fair amount of herbal teas (thereby taking essential oils internally as well) including fennel  and other aromatic plant teas.

FYI: However, the amount of fennel oil (and hence anethole) passing from comminuted or crushed fennel fruit into teas and aqueous infusions,- the time-honoured way of taking fennel fruit – is relatively low. It has been shown that only about 10% of the oil passes into a fennel tea infusion [Fehr 1982]. From the European Medicines Agency Post-authorisation Evaluation of Medicines for Human Use   **My own note: Fennel seeds contain 1-4% essential oil content so if you use 1 gram of dried fennel: how much essential oil would that be at 10%?  Answer correctly and you will receive the Aromatherapeutic Math Award for the year!

My goal is to shed some light on the subject.

Before entering this rather lengthy topic, let us clarify what internal use is.

Internal use of essential oils can mean a few things including:
  • Taking essential oil internally via the mouth
  • Utilizing suppositories (either vaginal or rectal)
  • And even swishing an essential oil based mouthwash around in the mouth
  • Utilizing essential oils in other orifices: nose (think nasya), ears, and eyes (not essential oils!)

And as an important note:
The German Commission E has approved specific essential oils for internal use.( These include the following:

Fennel (Foeniculum vulgare Miller var. vulgare (Miller)
is approved by the German Commission E for Peptic discomforts, such as mild, spastic disorders of the gastrointestinal tract, feeling of fullness, flatulence.  Catarrhs of the upper respiratory tract.  Its core actions include: Stimulation of gastrointestinal motility.  In higher concentrations, antispasmodic.  Experimentally, anethole and fenchone have shown a secretolytic action on the respiratory tract.

Fennel honey is recommended for catarrhs of the upper respiratory tract in children. Fennel honey is made by adding 0.5 grams of fennel essential oil to a kilogram of honey. Daily dosage is 10-20 grams a day.

Daily dosage of the essential oil is: 0.1 – 0.6 ml, equivalent to 0.1 – 0.6 g of herb.  Safety concerns: Fennel preparations should not be used on a prolonged basis (several weeks) without consulting a physician or pharmacist. The internal use of fennel essential oil is contraindicated during pregnancy (use herbal tea instead) and for infants/toddlers.

Anise (Pimpinella anisum L.) is used internally for dyspeptic complaints. Average daily dose of the essential oil is:  0.3 g for adults.

Caraway (Carum carvi L.) is indicated for Dyspeptic problems, such as mild, spastic condition of the gastrointestinal tract, flatulence and fullness.  Daily recommended dose is 3-6 drops. No contraindications listed.

Cinnamon bark (Cinnamomum verum J.S.  Presl syn.  C.  zeylanicum Blume) is indicated for: loss of appetite, dyspeptic complaints such as mild, spastic condition of the gastrointestinal tract, bloating, flatulence.  Its main actions include:  Antibacterial, fungistatic, and it promotes motility

Daily dosage is: 0.05 – 0.2 g of essential oil.  Safety: frequent allergic reactions on the skin and mucosa are noted. It is contraindicated during pregnancy and for those who have an allergy to cinnamon or peruvian balsam.  IMPORTANT NOTE: Cinnamon bark must be placed in an appropriate carrier oil and capsule to prevent burning of the digestive tract when taken internally!

Eucalyptus (Eucalyptus species including E. globulus, E. radiata) Internal and external:for catarrhs of the respiratory tract.  It is contraindicated when there is Inflammatory diseases of the gastrointestinal tract and bile ducts and for individuals with severe liver diseases. Average daily internal dosage is 0.3 – 0.6 g eucalyptus oil. Potential side affects, although rare, include: nausea, vomiting and diarrhea may occur after ingestion of eucalyptus preparations.

Lavandula flos. (Lavandula angustifolia) is indicated for internal use for: Mood disturbances such as restlessness or insomnia, functional abdominal complaints (nervous stomach irritations, Roehmheld syndrome, meteorism, nervous intestinal discomfort).  Daily dose is: Lavender oil: 1 – 4 drops (ca.  20 – 80 mg), e.g., on a sugar cube.


Medicine is typically measured in grams and milligrams.  There are 1000mg in 1 gram. According to my own measuring: 1 drop of essential oil can be (in general) .02 to .03 grams or 20-30 milligrams or 20000 micrograms (µg). Good thing to keep in mind when reading research papers.

So lets begin……..

We all take a certain amount of essential oils internally each day through our food and drinks. Essential oils and numerous components derived from them are widely use in many foods and beverages for flavoring and food preservation.

Essential oils from herbs and spices (oregano, sage, rosemary, thyme, etc.) have been used with an amount ranging from 0.1 to 1% EO volume per food weight (v/w) to reduce lipid oxidation of foodstuffs. It has been shown that the use of these EOs contributes also to the development of a pleasant odor and favorable taste to consumers. (Chemat, et. al.)

Essential Oils and individual components in Food Flavouring substances are used in processed foods and beverages to impart desirable organoleptic qualities and to provide the specific flavour profile traditionally associated with certain food products. Unlike many substances which are added to food to achieve a technological purpose, the use of flavouring substances is generally self-limiting and governed by the flavour intensity required to provide the necessary organoleptic appeal. Thus, flavouring substances are used generally in low concentrations resulting in human exposures that are very low. (

This paper goes on to state: 3.1  Structure-activity relationships and metabolic fate

Without exception, flavouring substances are volatile organic chemicals. The vast majority of flavourings ingredients have simple, well characterized structures with a single functional group and low molecular weight (< 300). More than 700 of the 1323 chemically defined flavouring substances used in food in the U.S. are simple aliphatic acyclic and alicyclic alcohols, aldehydes, ketones, carboxylic acids, and related esters, lactones, ketals, and acetals.

Other structural categories include aromatic (e.g., cinnamaldehydes and amhranilates), heteroaromatic (e.g., pyrazines and pyrroles) and heterocyclic (e.g., furanones and thiofurans) substances with characteristic organoleptic properties (e.g., furanones providing a strawberry note). For most flavouring substances, the structural differences are small. Incremental changes in carbon chain length and the position of a functional group or hydrocarbon chain typically describe the structural variation in groups of related flavouring substances. These systematic changes in structure provide the basis for understanding the effect of structure on the chemical and biological properties of a substance.

Toxicity is dependent on the chemical structure and metabolism of a substance. The “decision tree” procedure (Cramer  et al., 1978) relies primarily on chemical structure and estimates of total human intake to assess toxic hazard and to establish priorities for appropriate testing. The procedure utilizes recognized pathways of metabolic deactivation and activation, data on toxicity, and the presence of the substance as a component of traditional foods and as an endogenous metabolite. Substances are classified according to three categories:

Class I   –      Substances of simple chemical structure and efficient modes of metabolism which would suggest a low order of oral toxicity (e.g., butyl alcohol or isoamyl butyrate).

Class II  –      Contains structures that are intermediate. They possess structures that are less innocuous than substances in Class I, but do not contain structural features suggestive of toxicity like those substances in Class III. Members of Class II may contain reactive functional groups (e.g., furfuryl alcohol, methyl 2-octynoate, and allyl propionate).

Class III –      Substances of a chemical structure that permit no strong initial presumption of safety, or may even suggest significant toxicity (e.g., 2-phenyl-3-carbethoxy furan and benzoin).

The decision tree is a tool for classifying flavour ingredients according to levels of concern. The majority of flavouring substances fall into Class I because they are simple alcohols, aldehydes, ketones, acids or their corresponding esters, acetals and ketals that occur naturally in food and, in many cases, are endogenous substances. They are rapidly metabolized to innocuous products (e.g., carbon dioxide, hippuric acid, and acetic acid) by well recognized reactions catalyzed by cellular enzymes that exhibit high specificity and high catalytic efficiency (e.g., alcohol dehydrogenase and isovaleryl coenzyme A dehydrogenase). Substances that do not undergo detoxication via these highly efficient pathways (e.g., fatty acid pathway and citric acid cycle) are metabolized by reactions catalyzed by enzymes of low specificity and relatively low efficiency (e.g., cytochrome P-450 and glutathione transferase). For some groups of substances (e.g., branched-chain carboxylic acids, allyl esters, and linear aliphatic acyclic ketones), metabolic thresholds for intoxication have been identified (Krasavage  et al., 1980; Deisinger  et al., 1994; Jaeschke  et al., 1987). The dose range, over which a well-defined change in metabolic pathway occurs, generally correlates with the dose range over which a transition occurs from a no-observed-adverse-effect level to an adverse-effect level. For such groups of substances the dose range at which this transition occurs is orders of magnitude greater than the level of exposure from use as flavour ingredients.

Most substances in Class II belong to either of two categories; one includes substances with functional groups which are similar to, but somewhat more reactive than functional groups in Class I (e.g., allyl and alkyne); the other includes substances with more complex structures than substances in Class I, but that are common components of food. This category includes heterocyclic substances (e.g., 4-methylthiazole) and terpene ketones (e.g., carvone).

The majority of the flavouring substances within Class III include heterocyclic and heteroaromatic substances and cyclic ethers.

Many of the heterocyclic and heteroaromatic substances have sidechains with reactive functional groups. In a few cases, metabolism may destroy the heteroaromaticity of the ring system (e.g., furan).

Although metabolism studies have been performed for Class III flavouring substances with elevated levels of exposure, the metabolic fate of many substances in this structural class cannot be confidently predicted. Review of the group of substances in each of the structural classes indicates that as structural complexity increases (Class I – III), the number of flavouring substances and the levels of exposure decrease significantly (Table 3). In all structural classes, one-quarter or more of the flavouring substances are consumed at levels below 0.01 µg/day or 0.2 µg/kg bw/day.

According to the World Health Organization:

With regards to the aliphatic and alicyclic hydrocarbons (which includes, camphene, b-caryophyllen, d-limonene, myrcene, a-phellandrene, a-pinene, b-pinene, terpinolene, bisabolene, valencene, 3,7-Dimethyl-1,3,6-octatriene, gamma-3-carene, farnesense, b-bourbonene, cadinene and isomers, guaiene, and a few others). These compounds have been found in coffee, alcoholic beverages, baked and fried potatoes, bread, tea, and cheese. The substance with the highest natural occurrence is d-limonene.

The estimated daily per capita intakes of d-limonene in Europe and the USA are approximately 40000micrograms and 13000micrograms, respectively. Myrcene (No. 1327), a- and b-pinene (Nos 1329 and 1330, respectively), terpinolene (No. 1331), b-caryophyllene (No. 1324), a-phellandrene (No. 1328), and p-mentha-1,4-diene (No. 1340) account for most of the remaining (approximately 26–27%) total annual volume of production. The estimated daily per capita intakes of these flavouring agents are in the range of 92 to 8300mocrogams in Europe and 70 to 2400micrograms in the USA.

Absorption, distribution, metabolism and elimination
Being lipophilic, the aliphatic and alicyclic hydrocarbons in this group are likely to cross biological membranes by passive diffusion. After oral and inhalation exposure, they are rapidly absorbed and distributed to body tissues, elimination from blood being triphasic, with a slow terminal phase.

On the basis of the available data, it is anticipated that all the aliphatic and alicyclic hydrocarbons in this group will participate in similar pathways of metabolic detoxification in mammals, including humans.

After absorption, these hydrocarbons are oxidized to polar oxygenated metabolites via cytochrome P450 enzymes and alcohol and aldehyde dehydrogenases. The aliphatic and alicyclic substances are oxidized either by side-chain oxidation or by epoxidation of an exocyclic or endocyclic double bond. Alkyl oxidation initially yields hydroxylated metabolites that may be excreted in conjugated form or undergo further oxidation, yielding more polar metabolites that are also excreted in conjugated form in the urine. If a double bond is present, epoxide metabolites may form and these metabolites are
detoxified either by hydrolysis to yield diols, or by conjugation with glutathione.

In the class of aromatic hydrocarbons, essential oil components include: p-cymene, p-a-dimethylstyrene, biphenyl, 4-methylbiphenyl, and 1-methylnaphthalene.

Absorption, distribution, metabolism and elimination of aromatic hydrocarbons
Being lipophilic, the aromatic hydrocarbons in this group are likely to cross biological membranes by passive diffusion. Available data on pcymene and biphenyl indicate that these materials are readily absorbed from the gastro-intestinal tract, widely distributed in the body, metabolized and excreted mainly in the urine.

On the basis of the available data, it is anticipated that the aromatic hydrocarbons in this group will participate in similar pathways of metabolic detoxification in mammals, including humans. After absorption, these hydrocarbons are oxidized to polar oxygenated metabolites via cytochrome P450 enzymes and alcohol and aldehyde dehydrogenases. The major metabolic pathway of aromatic terpene hydrocarbons involves hepatic microsomal cytochrome P450- mediated oxidation of ring side-chains, yielding alcohols, aldehydes, and acids. The metabolites are then conjugated with glycine, glucuronic acid, or glutathione, and excreted in the urine and/or bile. The biotransformation of biphenyl proceeds via ring hydroxylation, preferentially at the C-4 position, yielding phenolic derivatives that are subsequently metabolized to glucuronide and sulfate conjugates, which are excreted in the urine.