Some of the molecules that make up essential oils can be neurotoxic.
However, it appears that in the same essential oil, neurotoxic molecules can be “neutralised” by molecules that are not and that will even protect the brain.
Definition
A neurotoxic substance is a substance that has a toxic effect exclusively on the nervous system. It disrupts or paralyses the functioning of neurons reversibly or permanently.
It causes disturbances such as
- vision problems or of other senses,
- of sleep and mood.
- motor or muscle coordination disorders (e.g. paralysis),
The risk is high by the oral route but lower by the dermal route.
The molecules at fault
Ketones such as menthone, carvone, verbenone, and camphor: these molecules trigger neuronal tissue damage and convulsions.
Monoterpenes: alpha-pinene; beta-pinene; alpha-terpinene: these molecules can also cause convulsions, but only at high doses. Avoid the oral route.
1.8 cineole (oxid): essential oils rich in 1.8 cineole are not recommended for children under 7 or even 12 years of age.
The case of ketones
The components of essential oils that are known to be neurotoxic belong to the ketone family.
Aromatherapy books often state that “all ketones are neurotoxic”. However, scientific studies on animal models, but also clinical trials, qualify this statement.
The toxicity of ketones is relative and depends on several factors:
- the nature of the ketone (some are more toxic than others: sesquiterpene ketones are much less toxic than the more aggressive monoterpene ketones);
- their degree of concentration in the essential oil;
- the doses used and the frequency of taking it;
- the administration route;
- the tolerance threshold: some people have a lower epileptogenic threshold;
- the age, the state of pregnancy or breastfeeding.
The signs of intoxication
The warning signs of acute poisoning are:
- vertigo,
- a feeling of being unwell,
- a sensation of disorientation,
- a lock of motor coordination.
Nausea is accompanied by loss of consciousness with respiratory discomfort or insufficiency and the appearance of psycho sensory disturbances.
Recommendations of usage
To limit the risks of potential neurotoxicity, the following recommendations are made:
Routes of administration
The cutaneous route is to be preferred. Toxicity by the cutaneous route is ten times lower than by the oral route. The EO must be diluted in oil without exceeding 6%.
Pregnancy, breastfeeding, child
Ketones cross the placental barrier and can cause convulsions which could be harmful to the pregnancy.
Ketones pass into breast milk.
Children are very sensitive to convulsive essential oils due to the immaturity of their central nervous system and the blood-brain barrier is less effective than that of an adult.
Use is strictly forbidden to pregnant or breastfeeding women, infants, children under 12 years of age and neurologically fragile people (all routes).
Do not use for too long a period (more than 3 weeks) and beware of overdosing.
Special cases
The individual tolerance threshold for ketones may vary greatly. Their use is limited in people with epilepsy
Their use is also forbidden in atmospheric diffusion or in aromatic baths for people with brain tumours.
The neurotoxic essential oils
Principal categories of ketones and their toxicity
The main accidents recorded concern the following essential oils:
- Hysope officinale (Hyssopus officinalis) : pinocamphone
- Sage officinale (Salvia officinalis) : thujone
- Rosemary camphor (Rosmarinus officinalis): camphor
- Mint pouliot (Mentha pulegium) : pulegone
- Blue Tansy
- Absinthe (Artemisia absinthium)
Moreover, as far as the oral route is concerned, the toxicity is unequal from one ketone to another depending on the EO:
Main ketones in decreasing order of toxicity
++++
a et β-thujone: Thuya occidentalis, sage officinalis
fenchone: Lavender stoechade (Lavandula stoechas), Fennel (Fœniculum vulgare var dulce)
pinocamphone, isopinocampone: Hysope officinale (Hyssopus officinalis)
pulegone: Mint pouliot (Mentha pulegium)
+++
cryptone (antifungal): Eucalyptus cryptone (Eucalyptus polybractea), red gum tree (Eucalyptus camaldulensis)
camphor (or borneone): Rosemary camphor (Rosmarinus officinalis CT borneone),
menthone: Peppermint (Mentha x piperita)
piperitone : field or wild mint (Mentha arvensis), Eucalyptus mint (Eucalyptus dives)
++
Lavender spike ((Lavandula latifolia)
verenone (hepatoprotective): rosemary verbenone (Rosmarinus officinalis CT verbenone)
β-diones: Helichrysum (Helichrysum italicum)
carvone: Carvi (Carum carvi), Dill (Anethum graveolens)
+
acetone: silver fir (Abies alba)
atlantone: Atlas Cedarwood (Cedrus atlantica)
List (non-exhaustive) of ketone essential oils:
dill (30 to 45 %), carvi (45 to 65 %), ladaniferous rockrose (5 to 10 %), coriander (4 to 6 %), curcuma (65 %), eucalyptus mint (35 to 40 %), eucalyptus cryptone (6 %), Fennel (3 to 5 %), geranium (6 to 9 %), helichrysum (10 to 15 %), hysope officinale (50 %), lavender spike (10 to 15 %), lavender stoechade (75 %), lavandin abrial (7 to 11 %), lavandin grosso (6 to 8 %), lavandin super (3 to 7 %), field mint (30 %), peppermint (32 %), mint pouliot (75 to 80 %, sometimes 90 %), spearmint (45 to 70 %), rosemary camphor (15 to 20 %), rosemary cineole (5 to 10 %), rosemary verbenone (10 to 15 %), sage officinalis (60 to 70 %), thuya occidental (70 %).
Abortive essential oils
Essential oils with ketones do not directly cause contractions, consequently, they are not abortifacient as such. Abortion would occur following the intoxication of the mother by these essential oils.
In general, neurotoxicity and abortifacient effect go hand in hand, considering that “the abortifacient molecules are globally the same as those responsible for neurotoxicity”, namely:
-
- a et β-thujone
- a et β -Pulegone
- pinocamphone
- camphor
- thymoquinone
- Menthone
- Verbenone
- Carvone
- Italidione
Moreover, it appears that other molecules, which are not ketones, should also be avoided during pregnancy.
For example: (E) Anethole (fennel EO), B-Elemene (Myrrh EO), methyl salicylate (Wintergreen) or Sabinyl acetate (i.e. Yarrow).
Ketones also have a hepatobiliary action, such as verbenone.
They induce a disintegration, a dispersion during prolonged olfaction or an accentuation of the memory (verbenone again).
Diketones have healing properties (Helichrysum italicum).
Tricetones are antibacterial and have a strong skin tropism (Manuka).
Main abortive essential oils:
Eucalyptus cryptone – Helicrysum – Lavender spike – Peppermint – Palmarosa – Parsley – Rosemary camphor – Rosemary verbenone – Sage officinalis – Thuya
Sources :
Faucon M., Traité d’aromathérapie médicale et scientifique, 2ème édition, Sang de la Terre, 2017, p. 116, 142.
