Tea Tree For Natural Insect Repellent

What is tea tree oil?

Tea tree oil (also called melaleuca oil) is an essential oil which is derived from tea tree (Melaleuca alternifolia) leaves. The tea tree is a part of the myrtle family, and is native to Australia, where it grows near streams and on forested wetland flats.

Note that the name ‘tea tree’ is also used for several other trees, which are closely related to the myrtle family, however Melaleuca alternifolia is the most relevant commercial species. Melaleuca alternifolia is also unrelated to tea plants, which are used to make black and green tea.

Like other essential oils, tea tree oil is made up of a diverse mixture of phytochemicals (i.e. natural substances synthesised in plants). A major component (around 35 – 48%)­¹ of tea tree oil is terpinen-4-ol, a type of terpene which is found in the leaves, bark, and branches of the tea tree. About 70 – 90% of tree tea oil content is composed of a mixture of terpinen-4-ol, γ-terpinene, and α-terpinene.¹ Tea tree oil also contains a mixture of other terpenes, such as limonene, sabinene, and viridiflorol. The oil can range in colour from pale yellow to clear and colourless and is accompanied by a fresh, camphor-like smell. When exposed to air, the oil oxidises, causing its chemical composition to change.

How is tea tree oil made?

Tea tree oil is extracted from Melaleuca alternifolia trees in Australia, where the plant is native. Commercial tea tree plantations arose in the 1970s and 1980s to support the global demand for tea tree oil, largely concentrated in New South Wales, Australia. Contemporary commercial production has since expanded to other countries including Tunisia, Vietnam, Malaysia, Egypt, and the United States, using other tree species which belong to the myrtle family.

What is tea tree oil used for?

Tea tree oil has many suggested uses and applications due to its various chemical and biological properties. These properties arise due to the characteristics of the phytochemical mixture comprising tea tree oil. Phytochemicals are highly diverse, naturally occurring substances which plants synthesise for many reasons, such as attracting pollinators, deterring herbivores, and resisting pathogens. This is why many compounds containing phytochemicals, such as tea tree oil, have antibacterial and antiseptic properties.

Tea tree oil is also known to behave as an antifungal, an antioxidant, and an anti-inflammatory. It is therefore often used in combination with treatments for acne, dandruff, lice, nail fungus, and athlete’s foot. However, the efficacy of tea tree oil for these purposes is disputed.

Another use for tea tree oil is as a natural insect repellent. This can include insects such as:

• Flies
• Ticks
• Mosquitoes
• Bees
• Ants
• Bed bugs
• Fleas

Tea tree oil as a mosquito repellent

More than 50% of the global population is at risk of contracting vector-borne diseases carried by mosquitoes. Malaria, dengue, West Nile Virus, Chikungunya, and filariasis are all examples of diseases which are carried and transmitted by mosquitoes. Mosquitoes are particularly prevalent in warm, humid climates such as the tropics, where they are active all year round. However, mosquitoes have a cosmopolitan distribution, meaning that they are well-adapted to a wide range of habitats found all over the world, with the exception of Antarctica. In cooler climates, mosquitoes may become more active and prevalent during summer.

DEET (N,N-diethyl-meta­-toluamide) is one of the oldest and most popular mosquito repellents. However, the use of DEET is not advised for women who are pregnant or breastfeeding, or for children less than three years old. Additionally, mosquitos are sometimes able to adapt to the use of DEET, making it ineffective.

Tea tree oil has been shown to be effective in controlling and repelling mosquitos. In fact, one study actually determined that tea tree oil was more effective than DEET in repelling mosquitos in study conditions, in addition to other essential oils such as rosemary, eucalyptus, and lavender essential oil. Using a blend of these essential oils therefore may represent an effective method of repelling mosquitoes.²

Another study used tea tree oil to develop several formulations which are effective mosquito repellents. These formulations were composed of a mixture of water, hydrogenated castor oil PEG-40, and tea tree oil, and were found to repel the activity of Aedes aegypti mosquitoes, demonstrating that tea tree oil has repellent properties.³

Tea tree oil for managing mites, and soothing mite-induced infections

Tea tree oil has reported miticidal (i.e. mite-killing) effects, which can be partly attributed to constituents such as terpinene-4-ol, 1,8-cineole, γ-terpinene, α-terpinene, and ρ-cymene. These compounds have anticholinesterase activity, meaning they can cause parasites to experience lethal muscular contractions and spastic paralysis, ultimately resulting in death. It has been suggested that the combination of these compounds in tea tree oil is more effective than applying these compounds individually.

A comprehensive literature review of the effects of tea tree oil on clinically important ectoparasites found that tea tree oil is effective in managing and repelling Demodex mites. This family of mites includes Demodex canis, Demodex folliculorum, and Demodex brevis, some of the most common, permanent ectoparasites in humans.

Currently, infection by these mites has no standard drug treatment, although several drug treatments exist which are approved for such usage, such as ivermectin and metronidazole. Of the existing treatment options, tea tree oil represents one of the more promising options in treating Demodex blepharitis, in which Demodex mites cause the eyelids to become itchy and swollen.⁴

Tea tree oil for managing scabies

Scabies is an example of another parasitic infestation caused by mites. In this context, mites burrow into the skin to lay eggs, resulting in extreme itchiness and rashes. Scabies can result in sores, and develop further into serious, lethal complications such as heart disease, kidney problems, and bloodstream infections (septicaemia).⁵

Although there are not many studies assessing the efficacy of tea tree oil against scabies mites, some evidence shows that treatments which are based on tea tree oil can be more effective than standard treatment options for scabies. Additionally, tea tree oil can be combined with other scabies treatments such as benzyl benzoate and permethrin, yielding better results than standard treatments alone.⁶

Efficacy of tea tree oil as an insect repellent

Although tea tree oil has been used historically to repel insects and help manage infections, its efficacy as an insect repellent is not always well-supported by clinical and scientific literature.

Many insect repellents which contain tea tree oil have been anecdotally reported as being highly effective. However, these repellents often use formulations which contain a mixture of several compounds, including other essential oils such as citronellol.

Some studies have found that insect repellents consisting of essential oil mixtures are effective for a mean duration of less than 20 minutes.⁷

Another study published in the Phytotherapy Research journal on 38 different essential oils, found that even at very high concentrations of 10 – 50%, essential oils were only able to prevent mosquito bites for up to two hours.⁸ Most commercial formulations contain essential oils at a concentration of 1 – 4%, since it is expensive and time-consuming to extract essential oils from plant extracts. Therefore, many products containing essential oils may not be effective as insect repellents.⁹

Insects such as mosquitoes have hundreds of different receptors, which they use to sense taste, odour, heat, and humidity. Although essential oils can block some of these receptors, preventing insects from detecting humans, repellents which are based on essential oils are often ineffective because insects can use other receptors which are not affected by essential oils. Additionally, essential oils which are effective against one species may not be effective against another, closely related species.

You should therefore always research a product online before purchasing it to use as an insect repellent. This is especially important if you live in, or are travelling to an area where there are insects which could be carrying vector borne diseases, such as dengue.

Toxicity and side effects

Similar to many other natural, plant-derived substances, tea tree oil can be harmful depending on its application and concentration.

The possible side effects of using tea tree oil include:

• Skin irritation, especially at higher concentrations
• Allergic skin reactions
• Poisoning: tea tree is poisonous if swallowed and has been known to induce comas

Tea tree oil can also be poisonous to cats and dogs. Applying large amounts of tea tree oil has been known to cause poisoning, and cause symptoms such as weakness, difficulties walking, muscle tremors, excessive salivation, and low body temperatures.

Always follow the directions on product labels, and be mindful of pets and vulnerable household members when using formulations which include tea tree oil.¹⁰

Summary

Tea tree oil is a natural, fragrant remedy with many applications. Anecdotal evidence suggests it can be effective in repelling mosquitoes, bed bugs, mites, and other insects. However, it is not clear how effective tea tree oil is as a general use insect repellent.

In addition, tea tree oil is poisonous if swallowed, and toxic to dogs and cats. It can also cause skin irritation and induce skin allergic reactions. You should therefore always be cautious when using formulations containing tea tree oil, and be mindful of potential adverse reactions.

Catherine Gudgeon

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