What are the potential skin hazards of tea tree essential oil?

The tea tree essential oil, extracted from the leaves of Melaleuca alternifolia, is primarily used for its antimicrobial and purifying properties. Its richness in terpenes, particularly terpinen-4-ol, accounts for its biological activity as well as its potency. Like any essential oil, it is a concentrate of active molecules capable of interacting directly with the skin barrier and cell membranes. This high concentration explains why the dangers of tea tree essential oil should not be underestimated, especially with repeated use. For information, the main adverse effects reported for tea tree essential oil are irritative reactions and contact dermatitis. The most common manifestations are redness, burning sensations, tingling or pronounced dryness. These side effects of tea tree essential oil are all the more likely in sensitive skin, atopic or already compromised.

Scientific literature confirms that tea tree essential oil is one of the essential oils most commonly implicated in cases of contact allergy.

Nearly one hundred clinical cases have been reported, emphasising that the hazards of tea tree essential oil are not merely anecdotal, even though they remain relatively rare in the general population. The chemical composition of tea tree essential oil partly accounts for its sensitising potential. Its main constituents include terpinen-4-ol, γ-terpinene, 1,8-cineole, α-terpinene, α-terpineol, p-cymene and α-pinene. When fresh, the oil is considered a weak to moderate sensitiser. However, its oxidation on exposure to air and light significantly increases its allergenic potency. Several oxidation products, such as ascaridole, terpinolene, α-terpinene and oxidised limonene, have been identified as major allergens. This chemical transformation explains the occurrence of certain allergic reactions to tea tree oil, particularly when the product is old or poorly stored.

Even though tea tree essential oil is often perceived as safe for occasional use, its high terpene concentration requires certain precautions. The side effects of tea tree oil are primarily irritant or allergic, the first rule remains dilution. Undiluted application is one of the main risk factors, especially on sensitive or damaged skin or in individuals predisposed to eczema.

In practice, it is advisable to dilute tea tree oil to a concentration of 1% to 5% in a carrier vegetable oil, such as jojoba oil or sweet almond oil.

Certain populations require increased vigilance. For instance, tea tree essential oil is contraindicated during pregnancy. As with most essential oils, that derived from the tea tree contains ketones which can trigger nervous or respiratory spasms that may increase the risk of miscarriage. As a precautionary measure, pregnant women are therefore advised to avoid tea tree essential oil, particularly during the first trimester.

The same caution applies during breastfeeding, as tea tree essential oil could come into direct contact with the infant. The skin barrier of children is more permeable than that of others, so great care must be taken with applied products. As a precaution, tea tree essential oil is contraindicated in this vulnerable population.

Another point of caution is product storage. As mentioned previously, the oxidation of the essential oil when exposed to air and light increases its allergenic potential, which can heighten the risk of an allergic reaction to tea tree oil. To mitigate these hazards, it is important to securely reseal the bottle after each use and to store it in a cool place, away from heat and light.

Caution should be exercised when inhaling or ingesting tea tree essential oil.

Indeed, inhalation of tea tree essential oil can irritate the respiratory tract, particularly in individuals with asthma. Ingestion, however, is strictly contraindicated without medical supervision. Even small amounts can impair the central nervous system, manifesting as ataxia, that is, coordination disorders, marked drowsiness, or even a state of hyporeactivity. In the most severe cases, respiratory complications such as inhalation pneumonitis have been reported. Data from animal studies also suggest possible hepatic and renal damage in scenarios of toxic exposure. Taken together, these elements emphasise that the dangers of tea tree essential oil are not limited to the skin and that its internal use should never be improvised.

• OSTERHOUDT K. C. & al. Ingestion of tea tree oil (Melaleuca oil) by a 4-year-old boy. Pediatric Emergency Care (2003).

• RILEY T. V. & al. Melaleuca alternifolia (tea tree) oil: A review of antimicrobial and other medicinal properties. Clinical Microbiology Reviews (2006).

• NIELSEN J. B. & al. A review of the toxicity of Melaleuca alternifolia (tea tree) oil. Food and Chemical Toxicology (2006).

• TATE B. & al. Allergy to tea tree oil: Retrospective review of 41 cases with positive patch tests over 4.5 years. Australasian Journal of Dermatology (2007).

• ANWAR F. & al. Essential oils used in aromatherapy: A systematic review. Asian Pacific Journal of Tropical Biomedicine (2015).

• SCHMIDT E. & al. Tea tree oil: Contact allergy and chemical composition. Contact Dermatitis (2016).

• KHAN I. A. & al. In chemico evaluation of tea tree essential oils as skin sensitizers: Impact of the chemical composition on aging and generation of reactive species. Chemical Research in Toxicology (2016).

• WOERDENBAG H. J. & al. Safety assessment and adverse drug reaction reporting of tea tree oil (Melaleuca aetheroleum). Phytotherapy Research (2022).

• LAUCHE R. & al. Efficacy and safety of Melaleuca alternifolia (tea tree) oil for human health – A systematic review of randomized controlled trials. Frontiers in Pharmacology (2023).

• BAYDAR T. & al. Safety and possible risks of tea tree oil from a toxicological perspective. Istanbul Journal of Pharmacy (2024).