Essential Oil Toxicity: The Complete Guide

Introduction

“All things are poison, and nothing is without poison; only the dose makes a thing not a poison.” PARACELSUS

For several decades, essential oils have enjoyed growing popularity among the general public and certain healthcare practitioners.

They are now used in hospitals, sold in pharmacies, specialty stores, and online.

This widespread use sometimes leads us to forget essential safety precautions and the potential toxic risks associated with essential oils.

WARNING: Never forget that aromatherapy is not a “gentle medicine.” It should always be used as a complement to medical advice. The use of essential oils is not intended to replace a medical consultation or diagnosis.

While (here in France) around fifteen essential oils fall under pharmaceutical monopoly due to their high toxicity, the vast majority are freely available and are often sold without clear information regarding their toxic risks.

It is therefore essential not to confuse one essential oil with another. Always ensure you know its exact name. Your source of information (blog, article, book…) must be reliable, as some sources lack sufficient precision in naming. It is also absolutely necessary to choose essential oils of adequate quality for topical application or oral use.

How to Identify a High-Quality Essential Oil

Safe and appropriate use, as well as prevention of aromatic toxicity, begins with the precise identification of the essential oil you intend to purchase.

This identification relies on both botanical identity and biochemical identity.

Botanical Identification

An essential oil is defined by the complete botanical identification of the distilled plant:

• Latin botanical name
• Plant part used
• Geographical origin (terroir)
• Cultivation method (preferably organic or wild-crafted plants)

Chemotypes and Biochemical Identity

Some plants can produce different essential oils depending on environmental conditions. Botanical identification alone is therefore not sufficient.

In the 20th century, Mr. Franchomme introduced the concept of the chemotype.

This concept is essential for species such as rosemary, thyme, and camphor trees.

The chemotype expresses the name of the molecule that allows the essential oil to be identified within its species, and which also possesses strong therapeutic value. This concept is crucial because it allows us to anticipate the indications and toxic risks of the essential oil.

Since then, the concept of chemotype has been extended to all essential oils and provides a guarantee of safety and a label of quality.

A chemotyped essential oil is a product whose aromatic molecules have been fully identified through chromatographic analysis.

Examples: Rosemary Essential Oil (Rosmarinus officinalis, also named Salvia rosmarinus)

Chemotype Camphor (Provence/Spain): analgesic and muscle-relaxant, but neurotoxic and abortifacient. Contraindicated for oral use and strictly contraindicated for pregnant or breastfeeding women, children, and individuals with epilepsy.

Chemotype Verbenone (Corsica): hepatic drainer, cholesterol-regulating, endocrine modulator. Mainly effective via sublingual use. Contraindicated for pregnant or breastfeeding women, children, and epileptic individuals.

Chemotype 1,8-Cineole (Morocco): respiratory oxygenating agent, mucolytic, antiviral. Best used topically or via inhalation. Poorly tolerated orally. Not recommended for pregnant or breastfeeding women, children, or asthmatic individuals.

The quality of an essential oil can easily be identified by:

Quality indicators of a good essential oil include:

• Packaging in dark glass bottles with a euro dropper cap
• A deep, pleasant, characteristic aroma
• Artisanal origin with strict traceability, harvesting and distillation standards, and biochemical identification

Toxicity According to Route of Administration

The most vulnerable populations are children, pregnant or breastfeeding women, individuals with epilepsy or asthma, and anyone taking medication or weakened by illness.

However, toxicity can affect everyone. The primary toxic risks associated with essential oils include skin and mucous membrane irritation or burns, as well as hepatotoxicity, neurotoxicity, and miscarriage risk.

Oral Use (Capsules)

This is the highest-risk route in terms of hepatotoxicity and neurotoxicity.

Overdosing or digestive sensitivity may cause gastric pain, which may improve with ingestion of sufficient amounts of vegetable oil.

At subtoxic doses, oral ingestion can be life-threatening (digestive hemorrhage, liver damage, nervous system impairment) and requires immediate hospital care.

Essential oils are concentrated forms of plant active ingredients, and two rules of caution apply: do not ingest them if you are unfamiliar with them, and use them diluted in a little vegetable oil. However, this does not mean that ingestion would be non-hazardous. There is also a potential risk of neurotoxicity and liver toxicity. See the list below in this article.

Sublingual Use

This route carries a high risk of dermocausticity. Dermocaustic essential oils must never be used sublingually.

This method also carries a potential risk of neurotoxicity. See the list below in this article.

Topical Use

Topical application exposes the user to risks of irritation, burns (also known as dermocausticity), or even allergic reactions.

The preferred method of use for dermocaustic essential oils remains oral administration, i.e. capsules. Irritating essential oils can be used orally or on the skin, but must always be diluted in a carrier oil before use.

The dilution percentage depends on the essential oil and the individual's sensitivity: diluted to 20%, most essential oils are generally well tolerated.

Allergic individuals, children, or anyone who has never used essential oils should always test them on the inside of their elbow before use (allergy test).

Topical application also carries a potential risk of neurotoxicity. See the list below in this article.

Respiratory Use

This method of use exposes the user to the risk of mucous membrane burns as well as neurotoxicity. This is why dermocaustic and neurotoxic essential oils should not be used in an atmospheric diffuser, especially if there is an epileptic person, a pregnant woman, or a young child in the household.

A list of neurotoxic and dermocaustic essential oils is provided further down in this article.

People suffering from asthma should generally avoid diffusing essential oils.

Safety Guidelines for Protecting Yourself from Toxic Risks

Beware of Mixing Essential Oils

In aromatherapy, it is recommended to mix essential oils together to increase their effectiveness. A blend of essential oils is called a synergy.

It's important to know that a synergy is more effective, but also potentially more toxic.

Vulnerable individuals, such as children, should not use blends containing too many different essential oils, especially several essential oils with the 1,8-cineole chemotype.

Camphor (or borneone) is a common molecule found in rosemary essential oil, lavender and lavandin essential oils, and camphor trees. It has analgesic, muscle-relaxant, and respiratory decongestant properties, but it is a highly neurotoxic ketone. Certain essential oils that contain significant amounts of camphor, and whose other molecules do not compensate for this danger, are strictly contraindicated for infants under 30 months, and even before 6 years of age, for individuals with epilepsy, and during pregnancy and breastfeeding.

Respect therapeutic breaks

Toxicity can also occur when essential oils are used daily without a break, regardless of the method of application.

These "therapeutic breaks" are intended to allow the body to eliminate the active ingredients.

When following an aromatherapy protocol over several months, it should therefore only be used 5 days out of 7, or 3 weeks out of 4.

Precautions for use

Some essential oils have specific toxicity:

For example, peppermint essential oil, due to its cooling effect, can burn the skin with an icy sensation if applied to too large an area. It is also contraindicated in cases of medication use, heart rhythm problems, or gallstones.

Another example would be Wintergreen essential oil, which has a warming effect that can be excessive if applied undiluted.

As you can see, some essential oils require specific precautions for use.

However, it is equally important to emphasize that essential oils have no side effects when used correctly and with full awareness of the individual's vulnerabilities.

Therefore, it is crucial to avoid self-medicating with essential oils on vulnerable individuals:

Babies and children, pregnant or breastfeeding women, people with asthma or epilepsy, and those taking other medications. These individuals have a much lower tolerance threshold and can easily be harmed by essential oils.

The practice of aromatherapy thus requires a minimum level of knowledge before applying and administering essential oils, which are highly concentrated aromatic molecules.

It is therefore strongly recommended to learn more through free introductory courses, dedicated programs, books, articles, or by consulting an expert in aromatherapy.

Why can essential oils be toxic?

Neurotoxicity: Ketones

Ketones are aromatic molecules with powerful pharmacological properties, but are toxic to the nervous system:

• Camphor (Borneon)
• Pulegone
• Fenchone
• Menthone
• Etc.

Even though they possess significant pharmacological value, they are very delicate to handle because they present a risk of neurotoxicity and miscarriage.

A neurotoxic essential oil, administered to a vulnerable individual (baby, pregnant woman, breastfeeding woman, or epileptic), can trigger a neurotoxic reaction very quickly. This risk exists whether administered via the skin, inhalation, or internal route. It can manifest after a single application or after several days of use, due to cumulative doses.

Symptoms of Poisoning

Toxicity will manifest as a series of symptoms such as:

• Apathetic state
• Drowsiness
• Nausea
• Vomiting
• Dizziness

Depending on the dose administered, this neurological alteration can lead to:

• Seizures
• Confusion
• Loss of consciousness
• Or even coma and death

Different Levels of Neurotoxicity

However, the risk should be qualified, as the toxicity of these molecules varies from one ketone to another, and therefore from one essential oil to another.

Toxicity also depends on the route of administration; for example, a ketone will be much more toxic when taken orally than if applied to the skin.

The type of ketone must also be taken into account. For example, italdione, present in Helichrysum (Immortella), is relatively non-toxic. Its use is therefore possible in infants after a fall or burn. However, the dosage and dilution must be adapted to the individual.

List of the Most Neurotoxic Essential Oils

Among the essential oils sold and available to the general public, here is the list of the most neurotoxic essential oils (next to it: the name of the ketone molecule in question):

• Sage (Salvia officinalis): thujone
• Thuja (Thuja occidentalis or orientalis): thujone
• Yarrow (Achillea millefolium): thujone
• All mint species (mentha): menthone, pulegone, and piperitone
• Eucalyptus Camphora : borneone
• Eukalyptus Camaldulensis : piperitone
• Eukalyptus Cryptone : cryptone
• Spike lavender (Lavandula latifolia): borneone
• Butterfly lavender (Lavandula stoechas): fenchone
• Rosemary ct. Camphor (Rosmarinus officinalis ct. camphor/borneon): borneone
• Cedarwood Atlas (Cedrus atlantica): atlantone

List of essential oils belonging (in France) to the pharmaceutical monopoly which require dispensing accompanied by advice and recommendations for precautions for use:

• Great wormwood (Artemisia absinthium L.)
• Small wormwood (Artemisia pontica L.)
• Common mugwort (Artemisia vulgaris L.)
• White mugwort (Artemisia herba alba Asso)
• Tree sagebrush (Artemisia arborescens L.)
• Canadian cedar or white cedar (Thuya occidentalis L.)
• Korean cedar (Thuya Koraenensis Nakai), known as “leaf cedar”.
• Hyssop (Hyssopus officinalis L.)
• Sage (Salvia officinalis L.)
• Tansy (Tanacetum vulgare L.)
• Thuya (Thuya plicata Donn ex D. Don.)
• Sassafras (Sassafras albidum [Nutt.] Nees)
• Savin (Juniperus sabina L.)
• Rue (Ruta graveolens L.)
• Vermifuge lambsquarters (Chenopodium ambrosioides L. and Chenopodium anthelminticum L.)
• Indian mustard (Brassica juncea [L.] Czernj. Et Cosson)

What to do in case of poisoning from neurotoxic essential oils?

If you experience symptoms suggestive of neurotoxicity (i.e., lethargy, nausea, vomiting, dizziness, etc.), stop taking the essential oil immediately.

If the essential oil was taken orally, it is recommended to take activated charcoal as soon as possible. If the neurotoxic essential oil was applied to the skin, unfortunately, there is not much you can do. Drink plenty of fluids to help flush out toxins and promote faster elimination.

In all cases, contact your local poison control center.

Dermocausticity, Hepatotoxicity: phenols and cinnamons

The phenol family, as well as aromatic cinnamaldehyde in certain cinnamon essential oils, present a dual toxic risk: skin and mucous membrane toxicity (dermocausticity) and liver toxicity (hepatotoxicity).

The precaution to take with essential oils is to avoid topical and rectal use; only oral administration (with vegetable oil in capsules) is possible.

In the case of a long-term protocol, to avoid any risk of hepatotoxicity, these essential oils should always be taken in decreasing doses, and treatment should be limited to a maximum of 10 days. Beyond this timeframe, the liver may experience some difficulties.

List of dermocaustic and hepatotoxic essential oils (=> not suitable for sublingual or topical route):

• Ajwain (Trachyspermum ammi or Carum copticum)
• Thyme ct. thymol (Thymus vulgaris ct. thymol)
• Clove (Syzygium aromaticum or Eugenia caryophyllata)
• All cinnamon essential oils (Cinnamonum cassia, aromatica vera or zeylanicum)
• Oregano (Origanum compactum and vulgare)
• Mountain savory (Satureja montana)

Photosensitivity

Some essential oils are photosensitizing (phototoxic), so prolonged sun exposure should be avoided for 6 to 8 hours after using the essential oil. The same applies to citrus fruit essences.

What is photosensitivity? It is a more or less severe sensitization of the skin, which can lead to erythematous, itchy, inflammatory, and potentially carcinogenic reactions.

List of photosensitizing essential oils:

• Angelica root (Angelica arcangelica)
• Cinnamon (Ceylon and Cassia) (Cinnamonum cassia, aromatica vera or zeylanicum)
• Citrus fruit essences (lemon, bergamot, kaffir lime, lime, orange, mandarin, grapefruit…)
• Petitgrain Mandarin (Citrus reticulata - leaves)
• Khella (Ammi visnaga)
• Tarragon (Artemisia dracunculus)
• Lavender (Lavandula angustifolia)
• Lovage root (Levisticum officinalis)
• Celery (Apium graveolens)
• Cumin (Cuminum cyminum)
• Verbena (Lippia citriodora)
• Rue (Ruta graveolens)
• Tagetes (Tagetes minuta)

Erythematous reactions that can promote carcinogenesis and accelerate melanogenesis may leave irreversible spots. Their internal use is also discouraged.

ADVICE: Avoid sun exposure for more than 15 minutes if essential oils (even diluted) have been applied to the skin in the 8 hours following application. This applies REGARDLESS OF THE ESSENTIAL OILS used. Indeed, any essential oil can trigger a PHOTO-ALLERGY reaction.

Another toxic risk

Administering essential oils containing high levels of monoterpenes, such as those found in all species of pine and fir, juniper, as well as white sandalwood, can, over time, inflame the nephrons; this risk is called nephrotoxicity.

However, if we listen to nature, these essential oils do not belong in the digestive system; they are meant to be inhaled and are intended for respiratory action.

Eucalyptol or 1,8 Cineol

Cineole is a molecule that is present in many essential oils and may trigger seizures in some predisposed individuals.

This molecule is also often poorly tolerated by people with respiratory sensitivities, such as asthmatics.

Here is a list of essential oils with a strong respiratory impact:

• Eucalyptus radiata
• Eucalyptus globulus
• Ravintsara (Cinnamonum camphora 1,8 cineol)
• Niaouli (Melaleuca quinquenervia)
• Laurel Leaf / Bay Laurel (Laurus nobilis)
• Cajeput (Melaleuca leucadendron or Melaleuca cajuputi)
• Myrtles (Myrtus communis)
• …

For example, Eucalyptus radiata contains 60 to 70% 1,8 Cineole, while Eucalyptus globulus contains 70 to 75%.

These subtle differences allow aromatherapists to refine their choice of essential oils in a blend intended for a child, minimizing the risk of toxicity.

The globulus variety is therefore best suited for adults, or at least children over 6 years old, especially since it can also have hormonal effects, while Eucalyptus radiata is more appropriate for younger children. This is why eucalyptus globulus essential oil is not recommended for atmospheric diffusion.

Some of these essential oils can be used with caution in young children, but others are strictly contraindicated. It is best to avoid self-medication with these essential oils and to follow the expert advice of a qualified aromatologist.

Precaution for vulnerable individuals

It is advisable to avoid self-medicating with essential oils in all the following vulnerable individuals:

Pregnant women

During pregnancy, the use of essential oils must be strictly supervised by an aromatherapist. Several precautionary rules must be followed to the letter to keep both mother and baby safe. Therefore, it is essential to avoid using essential oils on your own initiative without consulting a doctor or a qualified aromatherapist.

For your information, aromatherapy can improve the daily life of a pregnant woman, particularly in terms of circulatory, digestive, and psycho-emotional well-being. However, it is crucial to avoid using essential oils during the first three months of pregnancy, as the risk of birth defects is higher during this period.

All essential oils containing ketones are strictly contraindicated throughout pregnancy:

• All mint species (Mentha)
• Eucalyptus piperite or cryptone
• Spike lavender (Lavandula latifolia)
• Butterfly or French Lavender (Lavandula stoechas)
• Rosemary ct. Camphor (Rosmarinus officinalis ct. camphor/borneon)
• Sage (Salvia officinalis)
• Cedarwood Atlas (Cedrus atlantica)
• Non-exhaustive list

The effects of such essential oils, depending on the dose, can be abortive and neurotoxic. A simple sitz bath with a few drops of rue, savin, or thuja essential oil can already induce labor.

Avoid using essential oils containing phenols (thyme ct. thymol, clove, mountain savory, ajwain), as well as cinnamon essential oils, due to their caustic effects on the skin and liver.

Essential oils with estrogenic effects are also contraindicated.

During pregnancy, topical application and inhalation are the two preferred methods. However, avoid applying essential oils to the abdominal area.

To benefit from the olfactory route, prioritize atmospheric diffusion, as well as breathing in a blend of pregnancy-safe essential oils diluted to 10% or 20% from the inside of the wrists. Oral ingestion should be avoided.

Allergic individuals

Some aromatic molecules have allergenic potential. This is not toxicity, as this adverse reaction can occur even in trace amounts.

The allergic risk is primarily present with the use of essential oils on the skin. The reaction never occurs on the first contact but on subsequent ones. Extreme caution must be exercised with any use of essential oils by individuals with allergies.

Just because someone is allergic to a synthetic aromatic molecule found in hygiene or cosmetic products (for example, linalool, which perfumes many products) does not mean they will be allergic to an essential oil containing the same molecule. The whole, plant-based origin of essential oils often improves tolerance. However, caution is still advised, and essential oils should be tested beforehand.

Clinical expertise shows that some essential oils have a greater allergenic potential than others, such as:

• Laurel leaf / Bay laurel (Laurus nobilis)
• Cinnamon (Ceylon or Cassia/China) (Cinnamonum cassia, aromatica vera or zeylanicum)
• Inula (Inula graveolens or odorata)
• Pine (Maritime or Scots / Scotch Pine) (Pinus)
• Peppermint (Mentha piperita)
• Lavender (Lavandula angustifolia and other types)
• Sage (Sauge officinalis)
• Tolu and Peru Balm (Myroxylon balsamum)
• Copaiba (Copaifera officinalis)

The risk of allergic reaction is higher with skin contact than with internal use, but the latter is still possible.

If an individual is allergic to one essential oil, they may potentially react to others. The use of essential oils is therefore discouraged afterward.

The essential oil allergy test

It is advisable to perform an allergy test before using an essential oil or blend.

To do this, apply the blend to the inside of your elbow twice, 15 minutes apart, and observe for at least 48 hours to check for any redness or itching.

Delayed allergic reactions are possible. If a reaction occurs, do not use the tested product and consult an aromatherapist.

Children and babies

The nervous, respiratory, digestive, and dermatological immaturity of infants under 30 months makes them particularly vulnerable to essential oils.

The use of essential oils is not contraindicated, but precautions must be taken to manage the aromatic potency and avoid any adverse effects or toxic risks.

Therefore, the use of essential oils in children under 7 years old, without expert advice from a doctor or experienced aromatherapist, is strongly discouraged.

IMPORTANT: Peppermint essential oil is strictly contraindicated in babies under 30 months due to the risk of pharyngeal spasm (death by suffocation) => do not diffuse peppermint (Mentha piperita) or field mint (Mentha arvensis) essential oils.

Instructions for use in children

• Do not use essential oils on babies under the age of 3 months.
• Avoid using essential oils without medical advice on children under the age of 7 years.
• Never apply pure essential oils to a child's skin until they are 5 years old. Recommended dilutions are 10% to 30% depending on age, and only 5% for the youngest babies.
• Never administer essential oils orally or sublingually before the age of 7.
• Always perform an allergy test before using a new blend.
• Respect the recommended doses and durations of the protocol, and do not self-medicate. Refer to reliable sources for recommendations (pediatric books or articles).
• Do not use any neurotoxic essential oils or any essential oils containing phenols.
• Favor atmospheric diffusion, which is the simplest and least risky method (but do not run the diffuser while young children are nearby, and avoid diffusion altogether in case of asthma).

Asthmatics

He should avoid using essential oils containing 1,8-Cineole (eucalyptol). They should also avoid diffusing any essential oil in his home, as well as using steam inhalation with essential oils, as this can irritate the respiratory mucous membranes and trigger asthma attacks.

In case of an accident

If you have accidentally applied irritating or caustic oils to your skin, mucous membranes, or eyes: apply a generous amount of vegetable oil to the affected area as quickly as possible and absorb any excess with a paper towel.

In case of accidental ingestion of toxic substances, contact your local poison control center.

Conclusion

The toxic risks of essential oils are well known, and the safety precautions are reliable.

When used correctly, essential oils are completely free of toxic risk and even side effects.

Only those with allergies and those with pre-existing health conditions should exercise caution when using essential oils. Aromatic molecules have allergenic potential, which unfortunately limits their use.

Keep in mind that oral ingestion, combined with an overdose or a particular health condition, can lead to digestive intolerances, which may improve if taken with meals.

At subtoxic doses when ingested, these concentrated aromatic molecules can pose a life-threatening risk, such as liver or nervous system poisoning. In such cases, gastric lavage and medical attention from a poison control center are necessary.

Always remember to dilute essential oils in a carrier oil (not water) to improve tolerance, reduce irritation, and prevent skin irritation.

Essential oils are highly concentrated aromatic molecules. In most cases, they are effective when diluted in vegetable oil.

Diluting them in carrier oil not only slows down their absorption, but also improves skin and mucous membrane tolerance.

Dilution is absolutely indispensible with certain essential oils that are particularly irritating:

• All citrus essences (from zest) and conifer oils (pines and firs)
• All lemon-scented essential oils such as lemon litsea, lemon verbena and lemon eucalyptus
• Ylang-ylang (Cananga odorata)
• Tarragon (Artemisia dracunculus)
• Eucalyptus (Eucalyptus)
• Wintergreen (Gaultheria fragantissima and procumbens)
• All basil essential oils (Ocimum basilicum)

Examples of publications and studies on this topic

Tony Poirot. Bon usage des huiles essentielles, effets indésirables et toxicologie. Sciences pharmaceu-
tiques. 2016. HAL Id: hal-01732166
https://hal.univ-lorraine.fr/hal-01732166v1

Sartori Tamburlin I, Roux E, Feuillée M, Labbé J, Aussaguès Y, El Fadle FE, Fraboul F, Bouvier G. Toxicological safety assessment of essential oils used as food supplements to establish safe oral recommended doses. Food Chem Toxicol. 2021 Nov;157:112603. doi: 10.1016/j.fct.2021.112603. Epub 2021 Oct 12. PMID: 34648935.

Robert Tisserand, Rodney Young, Essential Oil Safety: A Guide for Health Care Professionals, 2013, Churchill Livingstone