TEA TREE OIL - TOXIC TO CATS
Copyright 1995, 2008 Sarah Hartwell

Tea Tree oil (oil of Melaleuca alternifolia, Oleum Melaleucae) is often promoted as pretty much the best thing since flu jabs as far as cats are concerned. It is a colourless or pale yellow oil obtained by steam distillation of the freshly harvested leaves of Melaleuca alternifolia (Australian Tea Tree). The main active ingredients are cyclic terpenes.

Tea Tree oil is promoted for the treatment of many skin problems and to control external parasites. Tea Tree oil lotions, shampoos and wipes are readily available from pet stores. It has been tested on humans and has been found to be effective on larger animals such as horses and sheep. In humans, it has been used in dentistry. However, animals and humans have been poisoned (sometimes fatally) from topical use or accidental ingestion of tea tree oil. Use of tea tree oil to control fleas has resulted in the death of kittens. The case studies open in a new window: Buddy and Foxy and Tiger and Miss Charlotte who were both made seriously ill.

2008: Cedar Oil, also being irresponsibly promoted as a natural flea treatment, is also highly toxic to cats and can be absorbed through the skin or licked from the fur and ingested. Laboratory toxicology demonstrate it to be poisonous.

The oil is reputed to have mild antibacterial and antifungal properties and is marketed as a natural remedy in veterinary and human medicine. It has proven antiseptic, antibacterial and fungicidal properties. It is sold in cat skin-care products for cleaning, healing, soothing and relieving itching associated with allergies, insect bites, hotspots, burns, abrasions, minor rashes and irritations. It is claimed that Tea Tree oil is an effective deodorizer, fur detangler, external parasite repellent and that it restores lustre to fur. It is actively promoted for its ability to penetrate the skin. The oil is highly lipophilic (attracted to fats, solvent) and is rapidly absorbed through intact skin (even faster through open wounds). It may also be ingested or absorbed orally through mucous membranes when a cat self-grooms.

Many cat owners claim to use Tea Tree oil without any adverse effect, however, there have been reports from the US that Tea Tree oil is toxic, to cats. There are unconfirmed reports of cats which have died following the its use. In the US, cat owners are advised to seek the advice of a vet before using the oil on cats. A Californian producer of the oil was reportedly unhappy about its Tea Tree product being promoted for use on cats due to concerns over its potential toxicity. In the UK there appears to be no mention of possible ill-effects or contra-indications and little awareness of its toxicity.

An American expert in the use of essential oils (who has used Tea Tree oil successfully to treat skin infections in cats) recommends that the oil should not be used where the cat can lick it off, This addresses the hazard of ingestion, but not of absorption through the skin or through wounds (such as unhealed flea bites).

In the early 1990s, it was suggested that cats with nerve disorders were unable to tolerate Tea Tree oil and suffered ill effects from its use. It was recommended that the amount of the oil in a product such as a cat shampoo should not exceed 1% although even that small amount may be toxic to certain individuals. American cat owners were advised not to use Tea Tree oil at all on cats with diabetes, epilepsy, metabolic or neurological disorders or on young kittens whose immature livers may not be able to cope with it.

Cases of Tea Tree oil poisoning have since been reported to the National Animal Poison Control Center (NAPCC) of the US following external application of the oil to cats. In most cases, the oil had been used at inappropriately high doses, causing acute poisoning. Symptoms occurred 2 - 8 hours after topical application of Tea Tree oil products. Symptoms were depression, weakness, ataxia, lack of coordination, behavioural disorders and muscle tremors. Warning signs may include vomiting, dizziness, clumsiness, lack of appetite and lack of energy.

Treatment is by removing residual amounts of oil from the skin by bathing the cat in a non-insecticidal shampoo. Intravenous fluids and glucose may were sometimes required to strengthen the animal, to overcome hypotension and to aid renal elimination (elimination in the urine). Where the oil had been ingested (licked off through grooming) activated charcoal and a cathartic was required to decrease the amount of oil absorbed in the gut. It has been reported that cats treated for Tea Tree oil poisoning recovered within 2-3 days following treatment of clinical signs and supportive care.

There is no specific antidote for the adverse reactions caused by dermal (skin) overexposure to Tea Tree oil (or related essential oils). Basic supportive care is required, including monitoring of respiratory and cardiovascular functions, checking for possible hypothermia and providing additional warmth if needed.

K Bischoff and F Guale reported a case of Australian Tea Tree (Melaleuca alternifolia) oil poisoning in three purebred cats. In brief, a Tea Tree Oil spot treatment/flea repellent was used on 3 Angora cats which had been shaved prior to treatment. The treatment was advertised for use as a topical treatment or a dip and was diluted according to manufacturer's instructions before use. Because the cats had been shaved, the treatment was applied directly to the skin.

Symptoms of Tea Tree Oil toxicity began five hours after treatment. Cat A became hypothermic, ataxic (lack of muscle co-ordination), unable to stand, but alert. Cat B became hypothermic, dehydrated and comatose. Cat C was alert but nervous, trembling and slightly ataxic. The three cats smelled of the Tea Tree Oil product. They were bathed using mild detergent to remove any residue from their skin, rehydrated, kept warm and treated for Tea Tree Oil ingestion. Their urine contained terpinen-4-ol (a constituent of Tea Tree Oil), indicating Tea Tree Oil ingestion. It also contained other substances which may have been metabolic breakdown products of Tea Tree Oil.

All three cats were given supportive nursing. Two recovered fully over a two day period. The worst affected (Cat B) remained dull, hypothermic, ataxic and dehydrated despite rehydration therapy. It appeared to rally on the third day of treatment, but died several hours later.

Not all vets or poison control centres are aware of the oil's specific toxicity to cats and the correct treatment may not be given. Vets are left to do the best they can based on the symptoms. Owners or groomers may not dilute the shampoos appropriately, Two cases in which Tea Tree Oil is implicated is that of Buddy, a six year old Maine Coon who became critically ill shortly after being bathed in a Tea Tree Oil shampoo and who died a few days later in great distress, and also of Foxy plus a 3 week old kitten treated for ringworm using Tea Tree Oil. Miss Charlotte and Tiger both became seriously ill after a Tea Tree shampoo was used to treat ringworm and a skin problems respectively. In the "Buddy" and "Foxy" case studies, the medications received are US brand names. There is no clinical evidence that Tea Tree Oil can cure ringworm in cats.

Tea Tree oil (melaleuca, Melaleuca alternifolia) is a phenol-containing essential oil. Its active ingredients are cyclic terpenes which have a similar structure and action to turpentine (a known toxin) - in fact Tea Trea oil makes a good paint solvent! Cats are uniquely sensitive to phenolics and other benzene-based compounds. Benzyl alcohol (a preservative) is toxic to cats.

The acute toxicity for the major terpenic compounds (linalool, ocimene, alpha-terpinene, 1,8-cineole, terpinolene, camphene) is 2 - 5 g/kg body weight, which is considered a moderately toxic range. From a toxicologic point of view Tea Tree oil is comparable to oil of  turpentine, which is readily absorbed from the gastrointestinal tract and skin. In addition, cats have relatively thin, delicate skin and Tea Tree oil is highly lipophilic (attracted to fats, solvent). This means that the oil is absorbed rapidly and enters the bloodstream. These factors may account for the poisoning cases reported to the NAPCC.

Cats are notoriously sensitive to toxins; their livers are not able to metabolize many substances which may safely be used on dogs (cats have been poisoned through use of dog flea preparations). For this reason, a substance shown to be beneficial and safe for humans may be unsuitable for use on cats. e.g. to cover the area where oil is applied.

Cats cannot efficiently metabolize substances present in certain essential oils (including Tea Tree oil), which will therefore build up in the cat's body. This means that they are not efficiently excreted by the body and can accumulate in soft tissues and vital organs. Over a period of time, the substances can reach toxic levels which cause death or symptoms of poisoning. An owner could therefore use Tea Tree oil in supposedly safe low concentrations for some time with no symptoms, though the cat is being slowly poisoned as the toxins accumulate. This is similar to they way that heavy metals (e.g. lead, zinc) or poly-chlorinated bi-phenols (PCBs) accumulate in the soft tissues and organs. An added danger is that cheap essential oils may be adulterated with other things for various reasons; the combination of substances could be more toxic than the unadulterated oil.

The other effects of long term use of Tea Tree oil on cats are not known, especially any carcinogenic (cancer-forming) effects. Nor is it confirmed whether it reacts with prescription medications or non-prescription items such as flea-treatments (sprays, powders and especially long-acting treatments added to the food or applied in absorbable form to the back of the neck). It is therefore recommended that Tea Tree oil is not used within days, possibly weeks, of other treatments.

I contacted a distributor of Tea Tree oil products in the UK with specific reference to potential toxicity of the oil (based on US studies). The company provided an information leaflet and although the oil appears useful in treating skin conditions and ecto-parasites (fleas, lice, mites etc) there is no scientific qualification for its effectiveness. The leaflet carried the following qualification:

It is worrying that a product is marketed for safe use on cats on the basis of anecdotal information related to humans, sheep and horses with no consideration given to the cat's poor ability to metabolize substances harmless to other species. It is of concern that the statements and claims made for the product are scientifically unproven. Herbal remedies used safely on humans for hundreds of years may be unsuitable for felines due to their different metabolism.

The leaflet claimed that the "absence of toxicity" and "general perfect tolerance" are attributes of Tea Tree oil. This conflicts with American reports and instances of poisoning reported to NAPCC. The leaflet also contained a list of Tea Tree oil constituents: alpha-terpinene, gamma-terpinene, cymene, alpha-terpineol, sesquiterpenes and up to 10% of cineole (British Pharmaceutical Codex, 1949). High levels of cineole may irritate mucous membranes, so low cineole oil is used for medicinal purposes.

Although the leaflet contained references to in vitro and in vivo studies, these were related to the oil's antimicrobial properties, not to its toxicity. The cat was not specifically mentioned. The idea of toxicology tests e.g. LD50 - lethal dosage - tests on cats will be abhorrent to cat owners, although the oil could be tested on feline cell cultures.

There is little toxicology data available on whole Tea Tree Oil to balance the enthusiastic marketing hyperbole and anecdotal claims. The following is taken from chemical data sheets on terpinen-4-ol (C₁₀H₁₈O), also known as terpinene-4-ol, (-)-4-isopropyl-1-methyl-1-cyclohexen-4-ol, 1-p-menthen-4-ol, 1-terpinen-4-ol, 4-terpinenol, 4-carvomenthenol, (+)-terpinen-4-ol, 1-methyl-4-isopropyl-1-cyclohexen-4-ol.

Tea Tree Oil contains upwards of 38% terpinen-4-ol. Data sheets state that it is harmful if swallowed and, in humans, is an eye, skin and respiratory irritant. It is a solvent of oil-base products e.g. plastics, rubber, oil based paints etc. It is absorbed rapidly and toxic effects noted in humans include central nervous system depression, seizures, coma and respiratory depression.

In humans, terpinen-4-ol has a toxicity of 4.3 g/kg, corresponding to a "completely safe" rating of between 3 and 5. One In rats, the lethal dose (LD50 - dosage at which 50% of subjects are fatally poisoned) is1.9 ml/kg (note: rats have relatively good liver function compared to that of felines). One promoter of Tea Tree Oil glowingly cites four cases of children swallowing up to 25 ml of Tea Tree Oil with no worse effects than mild diarrhoea and drowsiness which passed within 24 hours, but conveniently ignored a case where a patient remained in coma for 12 hours and semi-conscious for 36 hours following Tea Tree Oil ingestion.

Results of tests on humans do not prove that a product is suitable for cats since cats are very poor at metabolising toxic substances. For example, Aspirin is a useful painkiller in humans and well tolerated by most people, but it is highly toxic to cats. Since tea Tree oil can penetrate the skin and be ingested when a cat self-grooms, there is a possibility of it accumulating in the cat's liver and building up to toxic levels.

The UK distributors' leaflet presented only favourable information. It did not address the toxicity problem of Tea Tree oil or list the contra-indications if it is used. There was also no indication of whether the concentration of oil in the products was above the 1% 'safe' threshold recommended at the time the leaflet was issued. The distributors failed to explain why Tea Tree oil is promoted as safe and non-toxic in the UK but is considered toxic in the US. This is a case of irresponsible marketing and may already have led to 'mystery poisonings' or even deaths in cats and kittens.

For the sake of completeness, Tea Tree oil is not the only commonly found essential oil. Herbal remedies contain a variety of oils, a number of which are dangerous to cats. Problems commonly occur when an oil safe for use on humans or dogs are used on cats. Incorrect usage of an oil is almost guaranteed to cause problems. Problems also occur when an oil is 'in fashion' an marketed using anecdotal evidence; its effects on cats may not have been researched properly. Tea Tree oil is currently a fashionable remedy.

There have been cases of poisoning resulting from a single drop of an essential oil (not only Tea Tree oil, though this is the one most readily available to most cat owners) on their paws or belly, or diffusing them in the area where the litter box was located. Often the reaction was considered a "mystery poisoning" and the toxic agent was not readily identified. Many cat products now contain Tea Tree oil: shampoos, coat sprays, 'antiseptic' wipes, ear cleaners, rechargeable flea collars and herbal dips. Some are simply labelled as "herbal oils".

Essential oils which contain phenols are particularly toxic to cats and cause liver damage. These include Oregano, Thyme, Eucalyptus, Clove, Cinnamon, Bay Leaf, Parsley and Savory

Essential oils which contain ketones cause neurological symptoms. These include: Cedar Leaf*, Sage*, Hyssop*, Cyprus*, Lavender, Eucalyptus, Mint ,Caraway*, Citronella ,Clove*, Ginger*, Chamomile, Thyme and Rosemary (those marked * give particular cause for concern).

Cedar Oil, also marketed as a flea treatment, is also highly toxic to cats. It has been found to be toxic orally, when absorbed through the skin and an irritant if the fumes are inhaled (if the fumes are concentrated enough it may be absorbed through the lining of the lungs in toxic quantities). It is irresponsibly marketed by Cedarcide as safe for pets, but COSHH and toxicology data indicates it is toxic. Claims supporting Cedarcide are highly biased and were written for dog treatments (dogs have very different and more efficient liver function than cats). They are advertising claims, not scientific claims and perpetuate the misconception tha natural means "safe".

It is recommended that the oil is never be administered orally or used on the skin (cats will lick it off). It isn't known whether Tea Tree oil is safe for use by aromatherapy by nebulization, but it is recommended that it only be used in well-ventilated areas and that the cat be able to leave the room easily if it wishes (cats dislike strong odours).

For aromatherapy purposes, there is an alternative to the oil which is believed to be safe. A by-product of essential oil production is "hydrosol" (or "hydrolat"). Hydrosols are left behind after the essential oils are steam-distilled from plant matter. Steam is used to extract the essential oil from plant matter. The oil (containing the toxins) is condensed and removed, leaving the steam itself. The steam contains water-soluble plant compounds and can be condensed to form the hydrosol.

Classically, aromatherapy is the therapeutic use of essential oils. For purposes of aromatherapy for cats, hydrosols are considered safe for use on the skin because they don't contain the actual oil. They are delicately scented and have strong anti-inflammatory properties due to high levels of carboxylic acids. They are also soothing and act as gentle antiseptics. They are also believed to work on the emotions in the same way as Bach Remedies. It is important to locate a manufacturer who does not add essential oil to hydrosols to make it stronger smelling or more potent.

• Knight, M.J. & Villar, David. Toxicity of melaleuca oil and related essential oils applied topically on dogs and cats. Vet Human Toxicol 36(2): April 1994, p139-142.
• Florida Veterinary Scene Newsletter, 4(5), May/June 1995.
• Promotional leaflet from Pet & Garden Manufacturing plc (Scotland), 1995
• http://www.holisticat.com/aromatherapy.html
• http://www.holisticat.com/essoils_arch.html
• Case studies: Buddy; Foxy; Tiger; Miss Charlotte