Peppermint oil: dangers to be aware of?

Key points to remember.

Peppermint essential oil must always be diluted (≈ 5%) to prevent irritation.
Some isolated cases of contact dermatitis have been reported following the use of peppermint essential oil.
The high levels of menthol, menthone and isomenthone in peppermint essential oil confer upon it a neurotoxic potential in the event of overdose, justifying its contraindication during pregnancy, breastfeeding and in children under six years of age.
Certain conditions (atrial fibrillation, G6PD deficiency, asthma, epilepsy, liver disorders) require prior medical advice before using peppermint essential oil.
As with any active ingredient, we advise you to perform a patch test of peppermint essential oil on a small area of skin before adding it to your skincare routine.

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What is peppermint essential oil?

The peppermint essential oil is obtained from Mentha × piperita, a hybrid plant resulting from the cross between water mint (Mentha aquatica) and spearmint (Mentha spicata). It is typically extracted from the aerial parts of the plant, mainly the leaves, by steam distillation. This process allows the concentration of volatile aromatic compounds, yielding an essential oil very rich in active molecules, including menthol and menthone. Known since Antiquity, peppermint was already used for its digestive, stimulating and refreshing properties, as well as for its intense and distinctive scent.

Today, peppermint essential oil is utilised in a wide range of fields. In aromatherapy, it is valued for its toning and refreshing effect. In cosmetics, it is incorporated into purifying treatments designed to relieve heavy-leg sensations or even in hair-care products. Peppermint essential oil is also present in certain hygiene, food and household products.

What potential risks are associated with peppermint essential oil?

When correctly dosed, peppermint essential oil is generally considered safe.

However, like all essential oils, it remains a very potent concentrate of active molecules, which explains why adverse reactions related to peppermint essential oil can occur, particularly in individuals with sensitive skin. Furthermore, its main constituent, menthol, tends to stimulate cutaneous cold receptors, which can induce intense sensations of coolness, as well as tingling, burning or irritation when applied neat or insufficiently diluted.

Peppermint essential oil also contains allergens, which are likewise present in many essential oils, such as limonene or linalool, capable of triggering reactions of the type contact dermatitis. A review compiling studies conducted on more than 28,000 patients patch-tested with 2% peppermint essential oil in petroleum jelly showed that 0.6% of them exhibited an allergic reaction, mainly in the form of irritations. Although this percentage remains relatively low, it confirms the existence of side effects of peppermint essential oil, particularly in individuals with sensitive skin.

Furthermore, peppermint essential oilis not considered a sensitiser in the toxicological sense of the term. As a reminder, a sensitising substance can induce an allergic reaction after repeated exposure, even at low doses. This conclusion is based on the results of a Kligman test, a standardised protocol. Nevertheless, as with many essential oils, isolated cases of skin sensitisation have been reported, underscoring the importance of exercising caution.

Peppermint essential oil: what are the contraindications and precautions for use?

5.4%

Maximum concentration of peppermint essential oil not to be exceeded according to the book Essential Oil Safety: A Guide for Health Care Professionals.

This limit is primarily explained by the presence of pulegone and menthofuran in peppermint essential oil, both of which are potentially toxic compounds at high doses. In view of these risks, the authors further recommend completely avoiding its use in certain populations, particularly in individuals with cardiac fibrillation or those with glucose-6-phosphate dehydrogenase (G6PD) deficiency.

To minimise the risk of a cutaneous reaction, we also recommend that you perform a patch test before using any formulation containing peppermint essential oil. This involves applying a small amount of the product to the crook of the elbow and waiting 24 hours. The absence of redness, itching or a burning sensation is a reliable indicator of skin tolerance.

It should also be noted that peppermint essential oil exhibits neurotoxic potential, primarily due to its high content of menthol, menthone and isomenthone—molecules belonging to the ketone family. These compounds are capable of crossing the blood–brain barrier and, in cases of overdose or prolonged use, could disrupt the nervous system’s function by altering the myelin sheath that protects neurons.

For these reasons, peppermint essential oil is contraindicated during pregnancy, and is not recommended in breastfeeding women or in children under the age of six.

Finally, although the peppermint essential oil can be administered orally, it is preferable for this practice to be undertaken under medical advice, for a limited duration and at restricted doses (generally no more than three drops per day). Additionally, individuals with asthma, diabetes, epilepsy, liver disorders or hormone-dependent cancers must consult a healthcare professional before any use, as this essential oil may interact with certain medications and alter their efficacy.