Toxicity of Essential Oils: The Illusion of “Natural”, the Challenge of Quality
Although of natural origin, essential oils may present high toxicity depending on their chemical composition. Some are even restricted to pharmacy-only distribution. This article examines the risks associated with specific molecular families, the limitations of quality control in dispensing pharmacies, and the role — sometimes largely theoretical — of pharmacists in verifying certificates of analysis. It also reviews official reference frameworks (pharmacopoeia, AFNOR, ISO standards) intended to regulate EO quality, while highlighting their current limitations. Their complex composition and high concentration of active substances bring them closer to medicinal products than to simple natural consumer goods. Yet they are still widely associated with gentleness, wellness… and even safety. This perception is misleading and potentially hazardous. EO use, particularly in self-medication contexts, requires scientific and regulatory clarification, as some oils can be toxic or restricted to pharmaceutical dispensing.
Esméralda Cicchetti
7/7/20253 min read
Toxicity of Essential Oils: The Illusion of “Natural”, the Challenge of Quality
Essential oils (EOs), although of natural origin, are not risk-free. The role of chemotype knowledge in risk assessment has already been partly addressed (see blog article).
Their complex composition and high concentration of active substances bring them closer to medicinal products than to simple natural consumer goods. Yet they are still widely associated with gentleness, wellness… and even safety. This perception is misleading and potentially hazardous.
EO use, particularly in self-medication contexts, requires scientific and regulatory clarification, as some oils can be toxic or restricted to pharmaceutical dispensing.
Certain essential oils are regulated as potentially toxic substances
According to Article D.4211-13 of the French Public Health Code, 15 essential oils may only be sold by pharmacists. These are recognised for their significant toxicity: neurotoxicity, phototoxicity, irritant effects, or potential carcinogenicity.
However, this list does not imply that other essential oils are harmless. Toxicity depends on molecular composition, dose, route of administration, and the susceptibility of the exposed individual.
Emblematic case: terpenic derivative suppositories
In 2011, AFSAPS (now ANSM) issued a warning to healthcare professionals: suppositories containing terpenic derivatives — major constituents of essential oils — are contraindicated in children under 30 months and in those with a history of convulsions or epilepsy.
The reason is a documented risk of seizure induction associated with these compounds. This case clearly illustrates that natural molecules are pharmacologically active and therefore potentially dangerous in the absence of appropriate precautions.
Toxicity is determined by chemical composition
Essential oils are complex mixtures of several chemical families (monoterpenes, phenols, ketones, esters, lactones, etc.). Some of these families are highly effective therapeutically but also carry well-established risk profiles:
Phenols (e.g., thymol, carvacrol): strong antimicrobial activity, but irritant and potentially hepatotoxic at high doses
Ketones (e.g., camphor, thujone): mucolytic properties, but neurotoxic and potentially abortifacient
Furocoumarins (in citrus oils): phototoxic upon skin application
These risks are documented in scientific literature and regulatory frameworks (AFNOR, ISO, ANSM, among others).
Quality: a safety issue, not a marketing argument
Accurate knowledge of an essential oil’s chemical composition is therefore essential to assess its safety of use. This responsibility primarily concerns healthcare professionals, particularly pharmacists, who are expected to ensure the quality of substances used in community and hospital settings.
In theory, the pharmacist:
receives a certificate of analysis (COA) for each EO batch
verifies compliance with applicable standards (pharmacopoeia, AFNOR, ISO)
assesses the presence of allergens, solvents, and contaminants (pesticides, heavy metals, etc.)
In practice, according to Michel Faucon, these criteria are “often purely declarative” and rely on an excessive level of trust in suppliers. Certificates are rarely requested in pharmacies, and even less frequently critically reviewed.
Pharmacopoeia and standards: still incomplete coverage
The European Pharmacopoeia (11th edition) defines analytical criteria for only around thirty essential oils. This remains very limited compared with the hundreds of EOs used in aromatherapy.
These monographs include:
organoleptic assessment (odour, appearance, colour)
physicochemical tests (density, refractive index, optical rotation)
chromatographic analyses (GC-MS, HPLC) to identify active constituents and impurities (organic, inorganic, microbiological)
Due to this incomplete coverage, professionals often rely on additional references:
AFNOR standards (T75 A) in France
ISO standards (TC 54) internationally
These frameworks define reference chemical profiles for each EO in order to detect anomalies, adulterations, and counterfeits.
A future article will examine whether the control requirements defined in these standards are truly sufficient to ensure consumer safety, particularly given that end users are still not adequately supported by EO labelling practices (see blog article).
Conclusion: naturalness requires strict control
Beyond simplified narratives, the potential toxicity of essential oils is real, documented, and largely preventable — provided that professionals systematically verify composition and regulatory compliance.
However, this requires:
appropriate training
increased vigilance
systematic access to analytical quality data
Scientific rigour should not be an optional standard, but a baseline requirement for ensuring the safety of essential oil use.
For analytical support related to essential oils, contact us.
References
French Public Health Code. List of essential oils under pharmaceutical monopoly. Légifrance, 2007.
AFSAPS. Letter to healthcare professionals. ANSM, 2011.
ANSM. French Pharmacopoeia: preamble. ANSM, 2020.
