Tea tree oil, also known as melaleuca oil, is an essential oil that comes from the leaves and terminal branches of the tea tree, Melaleuca alternifolia. The oil is a colourless or pale yellow liquid. It contains over 100 compounds, including terpene hydrocarbons and associated alcohols. Use of the extracted oil, rather than the plant material itself, began in the 1930s, after the first published reports about its antimicrobial activity. Tea tree oil has antibacterial, antifungal, antiviral, antiprotozoal and anti-inflammatory activity. (Carson et al 2006)
The composition of tea tree oil is regulated by an international standard, which sets the maximum and minimum concentrations of 14 components. (ISO 2004) The oil should contain 30–48% terpinen-4-ol, 10–28% gamma-terpinene and up to 15% 1,8-cineole.
When exposed to light, air and heat, tea tree oil is degraded by oxidation, which produces oxidation products that contribute to the skin sensitising potential of the oil. (SCCP 2008) For human products, the European Cosmetic Toiletry and Perfumery Association (COLIPA) recommends: “To reduce the formation of these oxidation products, manufacturers should consider the use of antioxidants and/or specific packaging to minimise exposure to light” (COLIPA 2002).
Tea tree oil may be perceived and promoted as a ‘natural’ or ‘non-chemical’ treatment. The pure oil is readily available in ‘health food’ shops, typically in 10mL opaque bottles with a dropper top. Tea tree oil is an ingredient in numerous products for pets, including shampoos, creams, lotions, insect repellents and ear cleaners. None are licensed as medicines in the UK.
We found one published randomised controlled trial that evaluated the effect of tea tree oil, in the treatment of dermatitis, in dogs (Reichling et al 2004), and none evaluating it as a treatment for cats or its use to control fleas.
The double-blind randomised controlled trial evaluated a 10% tea tree oil cream in dogs. (Reichling et al 2004) In all, 57 dogs with localised dermatitis with or without pruritus were treated with tea tree oil cream or a control cream (a ‘commercial skin care cream containing antiseptic preservatives’), applied twice daily for 10 days. More dogs in the control group had a diagnosis of localised pruritic dermatitis (16 vs. 10 in the tea tree oil group) while more dogs in the tea tree oil group had severe dermatitis (8 vs. 1 in the control group). One adverse event was reported in the tea tree oil group but was not considered to be caused by the treatment. Five other dogs were withdrawn from the study: two due to lack of efficacy (one in each group), one due to non-compliance (tea tree oil group), one due to inappropriate inclusion (control group), and one due to a mild concomitant disease leading to exclusion (tea tree oil group). Efficacy of treatment, as judged by the veterinary investigator, was a measure of the change in severity between the start of the trial and day 10 or day 20. After 10 days, there was a significant difference between groups: 71% change in severity for the tea tree oil cream vs. 41% for the control cream, p = 0.04. However, the clinical differences between the dogs in each study group make it difficult to interpret the results of this trial.
The various constituents of essential oils in tea tree oil are highly lipophilic, and are relatively rapidly absorbed from the gastrointestinal tract and across the skin. (Villar et al 1994) The mechanism of the systemic toxicity of tea tree oil is unknown.
Signs of toxicity in companion animals occur within 2–8 hours of topical application of tea tree oil (Villar et al 1994). At first the signs can be non-specific and easily overlooked, but the breath, vomitus, urine and faeces may smell strongly of the oil. Clinical signs can include ataxia, weakness, tremors, behavioural disorders and depression. The oil can also irritate the skin and may cause erythema, dermatitis, pruritus and rash. Hepatic adverse effects may occur. In severe cases, there may be collapse, coma and convulsions. (Khan et al 2014) Because essential oils are volatile, they can be breathed in, causing aspiration pneumonia. (Wismer and Means 2012) Recovery often occurs within 24 hours, but can take longer.
Cats may be more at risk of adverse effects because their grooming behaviour may lead to a higher exposure after topical application (Khan et al 2014), and because metabolism of terpenes involves glucuronidation (Kohlert et al. 2000) and cats are poor glucuronide conjugators. (Khan et al 2014) Animals with liver disease may be at greater risk of toxicity because the oil constituents are metabolised by liver enzymes. (Villar et al 1994)
Products containing tea tree oil that are formulated for use on the skin or fur would not be expected to cause essential oil toxicity because the concentrations used are small.
Adverse effects have been reported in cats and dogs after the use of other ‘natural’ products containing essential oils for the control of fleas, even when the product was used as directed (Genovese et al 2012). This may be because treated animals groom excessively to try to remove an alien odour.
Tea tree oil is not known to interact with drugs, food or medicines. (Natural Medicines 2016)
There is limited information on the effects of tea tree oil in pregnancy and lactation in companion animals. In humans it is deemed ‘possibly safe’ when used topically and appropriately but is ‘likely unsafe’ when used orally. (Natural Medicines 2016) Foetal and maternal toxicity was seen in rats in a study of the embryofoetotoxicity of α-terpinene (Araujo et al 1996), which is present in tea tree oil at a concentration of about 10%. (Carson et al 2006)
Treatment of essential oil toxicity is supportive. Animals should be assessed for evidence of aspiration (which could occur after ingestion or possibly from grooming). Prognosis is good in animals with mild signs that resolve rapidly after contamination but, in animals with heavy contamination and neurological or prolonged signs that are failing to respond to supportive care, the prognosis is less certain.
- If the oil has been ingested, emesis is contraindicated because essential oils are volatile and there is a risk of aspiration pneumonia if vomiting occurs (Wismer and Means 2012). Activated charcoal is not likely to be an effective adsorbent for essential oils and could possibly precipitate emesis.
- If the tea tree oil has been applied dermally, the animal should be washed promptly with water and detergent because essential oils are not readily soluble in water. (Villar et al 1994)
- In animals with heavy contamination and significant signs of toxicosis, liver enzymes should be monitored. (Wismer and Means 2012)
- Diazepam or methocarbamol can be given for tremor or muscle fasciculation. (Khan et al 2014) Diazepam may be easier to give because it is available as an intravenous formulation and is licensed for use in dogs and cats, whereas methocarbamol is only available as tablets and not licensed for use in animals. Liver protectants could be considered in severe cases. (Khan et al 2014)
- Any dermal signs may be treated with antihistamines or corticosteroids, as needed. (Khan et al 2014)
The Veterinary Poisons Information Service collects information on adverse reactions to, and inappropriate use of, essential oils and can advise on appropriate management in a specific case. (See below for contact details)
There is very limited information on the use of tea tree oil in treating diseases in companion animals and so the benefits are uncertain. There is no evidence that tea tree oil is effective in controlling fleas.
Pure essential oils, including tea tree oil, should never be used on pets, either given by mouth or applied to the skin or fur. Deaths have been reported in pets after skin application of tea tree oil. Any pure essential oil on the skin should be washed off promptly with detergent and water. Even if the oil is applied diluted it may be ingested by the animal through grooming and cause toxicity. If the animal becomes unwell, contact a vet immediately. Pure essential oils should be stored safely out of sight, and out of reach of pets and children. The lid should be replaced securely, and any drips down the side of the bottle cleaned. ‘Natural’ does not mean safe.
Contact details for Veterinary Poisons Information Service in the UK:
Tel: 020 73 055 055 (emergency, 24 hours)
Tel: 020 7294 7561 (admin)
Email: firstname.lastname@example.org (non-emergency information)
Goal of activity: Update knowledge; help clinical decision-making
Authors/disclosures: Veterinary Prescriber editorial team/no conflict of interest
Specific learning objectives: to improve knowledge and understanding of the effects of tea tree oil in companion animals.
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Araujo IB et al. Study of the embryofoetotoxicity of alpha-terpinene in the rat. Food Chem Toxicol 1996; 34(5): 477-82.
Cosmetics Europe. COLIPA recommendation number 12: Use of tea-tree oil in cosmetic products. Brussels: Cosmetics Europe; 2002.
Genovese AG et al. Adverse reactions from essential oil-containing natural flea products exempted from Environmental Protection Agency regulations in dogs and cats. J Vet Emerg Crit Care 2012; 22(4): 470-5.
Khan SA et al. Concentrated tea tree oil toxicosis in dogs and cats: 443 cases (2002-2012). J Am Vet Med Assoc 2014; 244(1): 95-9.
Natural Medicines Comprehensive Database [Internet]. Tea tree oil monograph. Stockton: Therapeutic Research Faculty. Cited 31 July 2016. Available from naturaldatabase.therapeuticsresearch.com.
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Reichling J et al. Topical tea tree oil effective in canine localised pruritic dermatitis – a multi-centre randomised double-blind controlled clinical trial in the veterinary practice. Dtsch Tierarztl Wschr 2004; 111: 408-14.
Scientific Committee on Consumer Products (SCCP). Minutes 18th plenary meeting of the SCCP of 16 December 2008 (SCCP/1194/08). Opinion on tea tree oil (SCCP/1155/08).
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