Tea Tree - Melaleuca alternifolia

What is tea tree oil?

In the “Key facts” section of the EMA page on this substance, consulted on 01/10/2026, tea tree oil carries the Latin name “Melaleucae aetheroleum”, the English common name “Tea-tree oil” and the botanical name “Melaleuca alternifolia (Maiden and Betche) Cheel”. According to the ISO catalogue record, ISO 4730:2025 is titled “Essential oil of Melaleuca, terpinen-4-ol type (tea tree oil)”, is in its 4th edition, was published in 2025-06, has 9 pages, is at stage 60.60 “International Standard published” and falls under ISO/TC 54. The abstract of the same record states that ISO 4730:2025 specifies certain characteristics of this oil in order to facilitate assessment of its quality. In the “Life cycle” section of the record, the earlier editions ISO 4730:2017 and ISO 4730:2017/Amd 1:2018 are marked “Withdrawn”, and ISO 4730:2025 is marked “Published”.

Which species is the oil obtained from?

The EMA page on Melaleucae aetheroleum gives “tea tree oil” as the common name of the essential oil from the leaves and terminal branches of the trees Melaleuca alternifolia Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and other species of Melaleuca. Section 2 of the EU herbal monograph of the HMPC (EMA/HMPC/320930/2012, adopted on 24/11/2014) covers “Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum (tea tree oil)”, as an essential oil. The HMPC assessment report (EMA/HMPC/320932/2012, 2014) states that, according to the European Pharmacopoeia, the oil is obtained by steam distillation from the foliage and terminal branchlets of Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca. The addendum to that report (EMA/HMPC/765808/2022, 19/07/2023) states that the European Pharmacopoeia monograph had not been revised at that date and that its description of the oil includes Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca. The addendum also reports that, during the call for data, the Australian Tea Tree Industry Association (ATTIA Ltd) sent a submission asking for consideration of not including “…Melaleuca dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum…” in any revision of the monograph on Melaleucae aetheroleum (EMA/HMPC/120033/2022), to ensure alignment with an anticipated revision of the European Pharmacopoeia monograph on tea tree oil. The 2014 assessment report also relays the position of the Australian tea tree oil industry: the methyleugenol levels discussed in the report refer to Melaleuca bracteata, commercial tea tree oil is derived solely from Melaleuca alternifolia, and the industry’s own analytical surveys show that M. alternifolia contains only trace levels of methyleugenol.

How is the name Melaleuca alternifolia established?

In the World Checklist of Vascular Plants (WCVP, Kew), extract read on 01/10/2026, Melaleuca alternifolia (Maiden & Betche) Cheel is a name of rank “Species” with the status “Accepted”, placed in the family Myrtaceae. In the same extract, Melaleuca linariifolia var. alternifolia Maiden & Betche, of rank “Variety”, has the status “Synonym” and is attached to the accepted name Melaleuca alternifolia (Maiden & Betche) Cheel, with the homotypic synonymy flag “T”. The IPNI record 597833-1, read on 01/10/2026, gives the name Melaleuca alternifolia with the author “Cheel”, rank “spec.”, family Myrtaceae, the original remark “M. linariifolia, var. alternifolia, Maiden & Betche” and the place of publication “J. Proc. Roy. Soc. New S. Wales 1924, lviii. 195”. A record of the same citation in IPNI (114431-3) gives the citation type “comb. nov.”, the basionym Melaleuca linariifolia var. alternifolia Maiden & Betche and the publication year 1924. The 2014 HMPC assessment report also places the Melaleuca alternifolia tree in the botanical family Myrtaceae.

Which part of the plant is distilled, and how?

According to the EMA page, the oil is obtained by passing a current of steam through the fresh leaves and terminal branches; after cooling, the essential oil separates from the water and can be collected. The 2014 HMPC assessment report states that about 2 % essential oil can be obtained from the leaves of the “Australian Tea Tree” by extraction with a lipophilic organic solvent or by steam distillation.

What does the oil look like?

Citing Saller et al. (1998), the 2014 HMPC assessment report describes the oil as a clear, mobile, colourless or pale yellow liquid with no visible trace of water, an odour like turpentine, a high content of terpenes (> 50 to 60 %) and a specific weight of 0.89, almost insoluble in water but miscible with most organic solvents.

What is the composition of the oil?

According to the 2014 HMPC assessment report, the oil is composed of terpene hydrocarbons, mainly monoterpenes, sesquiterpenes and their associated alcohols, and a 1989 paper examining over 800 samples concluded that there were approximately 100 components (Brophy 1989). Citing Cox et al. (2000), the same report states that the oil consists largely of cyclic monoterpenes, of which about 50 % are oxygenated and about 50 % are hydrocarbons. Citing Bozzuto et al. (2011), the report gives for one oil sample, not described in the report (method not specified in the sentence), 42.35 % terpinen-4-ol, 3.71 % terpinolene, 3.57 % 1,8-cineole, 2.82 % p-cymene, 1.75 % limonene and 0.87 % myrcene. Citing Southwell (2006), the report states that p-cymene occurs naturally in the oil, typically at 0.5 to 8 %. Southwell et al. (2011), cited in the same report, quantified the traces of methyleugenol previously reported in the oil at between less than 0.01 % and 0.06 % (mean 0.02 %). For the oil they analysed, Table 1 of Mondello et al. (2006) (“Chemical composition of the Melaleuca alternifolia Cheel essential oil”) gives α-pinene (Kovats index 939) at 2.42 %, the authors stating that their quantitative data are based on peak area normalisation without a correction factor. For the same oil, Mondello et al. (2006) measured β-pinene (Kovats index 980) at 0.73 %, by the same peak area normalisation. For the same oil, Mondello et al. (2006) measured α-terpinene (Kovats index 1018) at 9.76 %, by the same peak area normalisation. For the same oil, Mondello et al. (2006) measured α-terpineol (Kovats index 1189) at 3.09 %, by the same peak area normalisation.

Which limits apply to terpinen-4-ol and 1,8-cineole?

Citing Carson and Riley (2001), the 2014 HMPC assessment report states that the Australian standard specified a 1,8-cineole content not exceeding 15 % and a terpinen-4-ol content above 30 %. According to the 2014 HMPC report, the European Pharmacopoeia and the International Standard ISO 4730, edition not stated in that sentence, require a minimum content of 30 % terpinen-4-ol and a maximum content of 15 % 1,8-cineole. Note 2 of section 2 of the HMPC monograph states that the material complies with the European Pharmacopoeia monograph of reference 01/2008:1837.

How does the oil change as it ages?

According to the 2014 HMPC assessment report, peroxides degrade over time, and degradation products such as 1,2,4-trihydroxymenthane may have a high irritation and sensitisation potential. Citing Southwell (2006), the report describes the peroxide value and the p-cymene content as particularly useful indicators of the age of the oil and of the extent of its degradation. The report adds that Southwell proposed monitoring the degradation status of the oil by using p-cymene as a reliable marker. The report states that the irritation potential of the oil may be related to its age, aged oils (presumably containing more peroxides and degradation products such as ascaridol) displaying a greater incidence of irritation.

What do animal and laboratory studies report?

Acute toxicity

According to the 2014 HMPC assessment report, the acute oral LD50 in rats has been reported as 1.9-2.6 ml/kg. Citing the SCCP (2008), the report states that no acute inhalation toxicity was evident in rats exposed to a mixture of tea tree oil, ethanol and CO2, but that methodological weaknesses of the study were noted. Citing the Council of Europe Committee of Experts on Cosmetic Products (2001), the report gives a dermal LD50 in rabbits above 5 g/kg. In its non-clinical conclusions, the report states that there are no oral repeated dose toxicity studies available for the oil.

Genotoxicity, carcinogenicity, reproduction

The non-clinical conclusions of the 2014 HMPC assessment report state that the oil was negative in the Ames assay on Salmonella typhimurium TA102, TA100 and TA98, with or without metabolic activation, and not genotoxic in mammalian cells in vitro at 95 µg/ml to 365 µg/ml (Pereira et al. 2014), and that it did not induce clastogenicity in the in vivo mouse micronucleus assay (Fletcher et al. 2005). The same report records that in December 2004 the Scientific Committee on Consumer Products (SCCP) noted that the oil is not mutagenic in the Ames test, while stating that the study details were insufficient and that the study was deemed inadequate. In its conclusions on clinical safety, the report states that the oil was not genotoxic in the in vivo mouse micronucleus test (up to 1750 mg/kg) and that the Ames test data are incomplete.

Under “Carcinogenicity”, the 2014 HMPC assessment report states that no data are available. The report states that tests on reproductive toxicity and on carcinogenicity have not been performed.

Skin irritation, sensitisation and phototoxicity in animals

Citing Nielsen (2005), the non-clinical conclusions of the 2014 HMPC assessment report state that the oil has been reported to cause mild to moderate skin irritation in rabbit studies, that LLNA studies indicate a mild skin sensitisation potential, and that highly degraded oil has a greater skin sensitisation potential because of oxidation by-products. In a published guinea pig test cited by the report, an oil of unknown quality gave positive reactions in 3 of 10 animals at an elicitation concentration of 30 %, results which, according to the report, may indicate that the oil may be a weak skin sensitiser. Citing Carson et al. (1998), the report states that undiluted oil did not produce phototoxic effects on the skin of hairless mice, although some irritation was observed.

How much more sensitising is oxidised oil?

In the local lymph node assay (LLNA) reported by the 2014 HMPC assessment report, run on two non-oxidised oil samples and one severely oxidised and degraded sample, the EC3 values were 24.3 % and 25.5 % for the two undegraded oils and 4.4 % for the degraded oil. The report concludes from this animal assay that undegraded oil has a weak sensitisation potential in this system, and that the degraded oil had 5-times higher potency but would still be regarded as a moderate sensitiser. In the section of the same report on human patch tests, Rutherford et al. (2007) are cited as concluding that oxidised oil has a sensitising capacity three times stronger than fresh oil. The report also states that fresh oil seems to possess only a weak sensitising potential, whereas oxidised constituents of the oil increase its ability to act as an allergen and as an irritant.

What is reported about skin reactions in humans?

Is 1,8-cineole an allergen?

Citing Carson and Riley (2001), the 2014 HMPC assessment report states that 1,8-cineole is probably an undesirable allergen in tea tree oil products. The same report states that 1,8-cineole was long regarded as an undesirable constituent because of its reputation as a skin and mucous membrane irritant, but that other studies suggested that it is not responsible for a large proportion of sensitivity reactions (Carson et al. 1998).

What do patch tests show?

Across the patch tests reviewed in the 2014 HMPC assessment report, 151 of 9367 subjects reacted positively to the oil, the rate of allergic reactions ranged from 0.6 % to 2.4 % depending on the study (mean 1.6 %), and the incidence and strength of reactions were generally higher with oxidised samples. In the same report, Nielsen (2005), citing Hammer et al. (2006), concluded that the prevalence of positive findings among pre-sensitised dermatological patients in clinical studies is generally around 0.4 %-0.6 %, which would give the oil only a weak sensitising potential in pre-sensitised people, a figure that may be an overestimate because of aged oils and selection bias. The report states that undiluted oil has been reported to cause skin irritation in a small proportion of subjects (generally < 5 %).

Which adverse reactions have been reported?

The 2014 HMPC assessment report states that forty-six cases of allergic contact dermatitis associated with the oil were reported in the literature from 1991 to 2004, mostly limited to mild symptoms such as erythema and pruritus, or an eczematous plaque at the area of application. The report states that burn-like skin reactions have been reported in Denmark, at a rare frequency (< 1/1000). Citing the Norwegian Food Safety Authority (2012), the report states that the oil cross-reacts with colophony. In its conclusions on clinical safety, the report states that the reported adverse events were minor and mostly limited to local irritation. According to the 2023 addendum, a search of EudraVigilance found 3 cases: in one, the patient was receiving 8 medicines, so that the effects could not be directly related to the oil; the two others involved the oil alone and led to facial swelling, rash, pruritus, asthma and dermatitis, which disappeared after withdrawal, the causal relationship being assessed as possible.

What is reported about poisoning in humans?

Citing Carson and Riley (1998), the 2014 HMPC assessment report states that several cases of human poisoning by the oil have been reported, mostly involving ingestion of modest volumes (10-25 ml), and that in two cases ingestion resulted in what appeared to be systemic contact dermatitis. According to the report, accidental poisonings by ingestion show that at relatively high doses the oil causes central nervous system depression and muscle weakness, symptoms that had generally resolved within 36 hours. Citing the 29th annual report of the National Poison Data System of the American Association of Poison Control Centers (Bronstein et al. 2012, 2011 data), the report states that among 1,376 exposure cases, no or minor outcome was reported in most cases, a minor outcome in 192 cases, a major outcome in 5 cases, and no death.

What poisonings have been documented in animals?

Cats in the HMPC report

Citing Bischoff and Guale (1998), the 2014 HMPC assessment report describes a published case of poisoning after a single dermal application of 120 ml of undiluted oil to 3 adult female Angora cats, one of which died; all 3 showed hypothermia, incoordination, dehydration and trembling, and the 2 survivors recovered after 1 to 2 days. The report states that neurotoxicity and death have been observed in cats exposed dermally to very high doses of the oil, and that oral exposure through licking of the skin and fur of the application area cannot be ruled out for these animals.

Dogs and cats in a poison control centre case series

Khan et al. (2014, J Am Vet Med Assoc) conducted a retrospective case series of 337 dogs and 106 cats exposed to 100 % tea tree oil, with incident data from the ASPCA Animal Poison Control Center database from January 2002 to December 2012. In this series, the oil had been used intentionally in 395 of the 443 animals (89 %), in amounts ranging from 0.1 to 85 mL. The exposure route was cutaneous in 221 animals (50 %), cutaneous and oral in 133 (30 %) and oral in 67 (15 %). Clinical signs appeared within 2 to 12 hours and lasted up to 72 hours; the most common were increased salivation, signs of central nervous system depression or lethargy, paresis, ataxia and tremors. The authors found a significant association between severity of illness and age and weight, with a higher prevalence of major illness in younger and smaller cats. The authors conclude that intentional or accidental use of 100 % oil in dogs or cats caused serious signs of central nervous system depression, paresis, ataxia or tremors within hours, lasting up to 3 days, and state in their discussion that such use can result in severe neurological effects (paresis, ataxia, tremors, coma) or death.

A cockatiel case

Vetere et al. (2020, BMC Vet Res) report a one-year-old male cockatiel (Nymphicus hollandicus) of 80 g presented for a severe depression episode of about 4 h, after 0.15 ml of 100 % pure tea tree oil (species written “Melaleuca alternifoglia” in the article) was applied directly to the skin of its right wing and part of its thorax. According to the owner, as reported by the authors, the bird suffered convulsions and vomiting for about 15 min before entering a comatose state, the symptoms having appeared 30 min after the application. The authors write that the literature described no case of Melaleuca oil poisoning in pet birds, but that such poisoning has been reported in humans (mainly by ingestion) and in dogs, cats and rats.

How is the oil identified in registers?

The ECHA CHEM record 100.077.588, consulted on 01/10/2026, lists “Melaleuca alternifolia, ext.” with EC number 285-377-1 and CAS number 85085-48-9, described as extractives and their physically modified derivatives (tinctures, concretes, absolutes, essential oils, oleoresins, terpenes, terpene-free fractions, distillates, residues, etc.) obtained from Melaleuca alternifolia, Myrtaceae. The same record gives the tonnage band “100 - 1,000 tonnes”, the regulatory processes “REACH pre-registration”, “EC Inventory”, “REACH registration” and “CLP notification”, and the mention “REACH REGISTERED”. On the same date, an ECHA CHEM search for CAS number 68647-73-4 returned three records: 100.169.204 “Melaleuca Alternifolia (Tea Tree) Leaf Oil” (EC 641-387-1, CAS 68647-73-4), 100.120.776 “Extract from tea tree” (EC 614-679-1, CAS 68647-73-4) and 100.077.588 “Melaleuca alternifolia, ext.” (EC 285-377-1, CAS 85085-48-9). In that search, record 100.120.776 “Extract from tea tree” carries, among its regulatory processes, the code “EU-PLANT_PROTECTION-ANX_ACTIVE”.

What does EU cosmetics law say about limonene, alpha-terpinene, terpinolene, terpineol and pinene?

Regulation (EU) 2023/1545 replaces entry 88 of Annex III of Regulation (EC) No 1223/2009: limonene (dl-limonene or dipentene, CAS 138-86-3; d-limonene, CAS 5989-27-5; l-limonene) is to be indicated in the list of ingredients above 0.001 % in leave-on products and 0.01 % in rinse-off products, and the peroxide value of each substance is set below 20 mmoles/L. Under Regulation (EU) 2023/1545, replaced entry 131 of Annex III of Regulation (EC) No 1223/2009 provides that the presence of alpha-terpinene (p-Mentha-1,3-diene, marked with note (*2); CAS 99-86-5, EC 202-795-1) is indicated in the list of ingredients when its concentration exceeds 0.001 % in leave-on products and 0.01 % in rinse-off products, and sets its peroxide value below 10 mmoles/L. The same regulation replaces entry 133: terpinolene (p-Mentha-1,4(8)-diene, marked with note (*2); CAS 586-62-9, EC 209-578-0) is to be indicated in the list of ingredients above 0.001 % in leave-on products and 0.01 % in rinse-off products, with a peroxide value below 10 mmoles/L. Under note (*2) of the annex, cosmetic products containing the substance concerned that do not comply with the restrictions may, provided they comply with those applicable on 15 August 2023, be placed on the Union market until 31 July 2026 and made available on that market until 31 July 2028. Under the same regulation, entry 343, added to Annex III, provides that the presence of terpineol (including p-Menth-1-en-8-ol (alpha-Terpineol), chemical names marked with note (*4); CAS 8000-41-7/98-55-5/138-87-4/586-81-2) is indicated in the list of ingredients when its concentration exceeds 0.001 % in leave-on products and 0.01 % in rinse-off products. Under the same regulation, entry 371, added to Annex III, provides that the presence of pinene (alpha-Pinene and beta-Pinene, marked with notes (*4) and (*5); CAS 80-56-8/7785-70-8/127-91-3/18172-67-3) is indicated in the list of ingredients when its concentration exceeds 0.001 % in leave-on products and 0.01 % in rinse-off products, and sets its peroxide value below 10 mmoles/L. Under note (*4) of the annex, cosmetic products containing the substance concerned that do not comply with the restriction(s) may be placed on the Union market until 31 July 2026 and made available on that market until 31 July 2028. Under note (*5) of the annex, the substance concerned, being a monoterpene, is subject to the restriction on peroxide value set out in entry 130.

References

• European Medicines Agency (EMA), « Melaleucae aetheroleum - herbal medicinal product », web page, consulted 01/10/2026 — https://www.ema.europa.eu/en/medicines/herbal/melaleucae-aetheroleum
• International Organization for Standardization (ISO), catalogue record « ISO 4730:2025 — Essential oil of Melaleuca, terpinen-4-ol type (tea tree oil) », edition 4, 2025-06, archived copy of 07/12/2025 (Internet Archive) — https://web.archive.org/web/20251207052039id_/https://www.iso.org/standard/88587.html
• European Medicines Agency, Committee on Herbal Medicinal Products (HMPC), « European Union herbal monograph on Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum », Final, EMA/HMPC/320930/2012, dated 24 November 2015 (HMPC adoption 24/11/2014) — https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-melaleuca-alternifolia-maiden-and-betch-cheel-m-linariifolia-smith-m-dissitiflora-f-mueller-and-or-other-species-melaleuca-aetheroleum-first-version_en.pdf
• European Medicines Agency, Committee on Herbal Medicinal Products (HMPC), « Assessment report on Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum », Final, EMA/HMPC/320932/2012, 24 November 2014 — https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-melaleuca-alternifolia-maiden-and-betch-cheel-m-linariifolia-smith-m-dissitiflora-f-mueller-andor-other-species-melaleuca-aetheroleum-first-version_en.pdf
• European Medicines Agency, Committee on Herbal Medicinal Products (HMPC), « Addendum to Assessment report on Melaleuca alternifolia (Maiden and Betche) Cheel; Melaleuca linariifolia Smith; Melaleuca dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum », EMA/HMPC/765808/2022, 19 July 2023 — https://www.ema.europa.eu/en/documents/herbal-report/addendum-assessment-report-melaleuca-alternifolia-maiden-and-betche-cheel-melaleuca-linariifolia-smith-melaleuca-dissitiflora-f-mueller-andor-other-species-melaleuca-aetheroleum_en.pdf
• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip
• International Plant Names Index (IPNI), name record 597833-1 « Melaleuca alternifolia Cheel » (Myrtaceae), consulted 01/10/2026 — https://www.ipni.org/api/1/n/597833-1
• Khan S.A., McLean M.K., Slater M.R., « Concentrated tea tree oil toxicosis in dogs and cats: 443 cases (2002–2012) », Journal of the American Veterinary Medical Association 2014;244(1):95-99, doi:10.2460/javma.244.1.95 — https://avmajournals.avma.org/view/journals/javma/244/1/javma.244.1.95.xml
• Vetere A., Bertocchi M., Pelizzone I. et al., « Acute tea tree oil intoxication in a pet cockatiel (Nymphicus hollandicus): a case report », BMC Veterinary Research 2020;16:29, doi:10.1186/s12917-020-2255-4 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=6995176
• European Chemicals Agency (ECHA), ECHA CHEM, substance record 100.077.588 « Melaleuca alternifolia, ext. » (EC 285-377-1; CAS 85085-48-9 and 68647-73-4), consulted 01/10/2026 — https://chem.echa.europa.eu/api-substance/v1/substance/100.077.588
• European Chemicals Agency (ECHA), ECHA CHEM, search for CAS 68647-73-4, consulted 01/10/2026 — https://chem.echa.europa.eu/api-substance/v1/substance?pageIndex=1&pageSize=10&searchText=68647-73-4
• Commission Regulation (EU) 2023/1545 of 26 July 2023 amending Regulation (EC) No 1223/2009 of the European Parliament and of the Council as regards labelling of fragrance allergens in cosmetic products — https://publications.europa.eu/resource/celex/32023R1545
• Mondello F., De Bernardis F., Girolamo A., Cassone A., Salvatore G., « In vivo activity of terpinen-4-ol, the main bioactive component of Melaleuca alternifolia Cheel (tea tree) oil against azole-susceptible and -resistant human pathogenic Candida species », BMC Infectious Diseases 2006;6:158, doi:10.1186/1471-2334-6-158 — https://bmcinfectdis.biomedcentral.com/counter/pdf/10.1186/1471-2334-6-158.pdf