What Is Tea Tree Oil, What Does It Do? Composition and Allergy Risk
Other names: Melaleuca Alternifolia (Tea Tree) Leaf Oil, Melaleuca Alternifolia Leaf Oil, TTO
Tea tree oil is a volatile oil distilled from the leaves of Melaleuca alternifolia, whose main component is terpinen-4-ol. Its effect against microbes is shown in the lab, while human data on dandruff and acne rest on small studies. Once it deteriorates in air, its allergenic potential increases, and in the EU low concentrations are recommended depending on the product type.
At a glance
- INCI name
- Melaleuca Alternifolia (Tea Tree) Leaf Oil
- Main component
- Terpinen-4-ol, ISO 4730:2017 range 35-48%
- Scientific upper limit in the EU
- Shampoo 2%, shower gel and face cleanser 1%, face cream 0,1%
- Classification in the EU
- Reproductive toxicity 1B, based on animal data; process ongoing
- Caution
- Not applied neat, not swallowed; a spoiled oil is riskier
What's on this page?
The name tea tree is misleading: the plant has no connection with the tea drunk. It is a volatile oil steam-distilled from the leaves and twigs of the Australian Melaleuca alternifolia tree. It is not a single substance but a mixture of dozens of monoterpenes and related compounds. In skin care its most cited use is acne. The evidence for acne and the comparison with benzoyl peroxide are covered in the tea tree oil and acne article; this page looks at the oil itself: its composition, where else it has been tested, why it becomes risky once spoiled, and why it is debated in Europe.
Terpinen-4-ol and ISO 4730: How to read the composition?
There is an international standard that defines quality: ISO 4730. It shows whether the oil really is of this type and the balance of its components. A new edition of the standard was published in 2025; the ranges below are from the latest 2017 edition that could be reached.
| Component | Approximate value | Why does it matter? |
|---|---|---|
| Terpinen-4-ol | %35-48 | Seen as the main carrier of antimicrobial effect |
| 1,8-Cineole | At most 10% | Excess may indicate low quality |
| Alpha-terpinene | Variable | Spoils quickly in air, forming allergenic products |
| p-Cymene | Low; rises in old oil | A sign of spoilage; also under regulatory attention |
Writing "tea tree" on the label does not state the proportion, nor does it show whether the oil meets the standard. On a pure-oil product the ingredient is a single line; but in a cosmetic product, seeing only Melaleuca Alternifolia Leaf Oil as a name does not tell you what percentage it is.
Where else has it been tested, apart from acne?
| Area | Study | Result | Its limit |
|---|---|---|---|
| Dandruff | 126 people, 5% shampoo, daily, 4 weeks, single-blind | Severity score fell by 41%, with placebo 11% | Among the groups that can be understood from the odour, only 1 people in each group were completely cleared; sector-funded |
| Demodex mite on the eyelid | Eyelid cleansing, comparison of 160 people | Mite count fell from 4,0 to 3,2, complaint score decreased | Do not apply to the area around the eye on your own: in a series of 11 people, 3 showed marked irritation |
| Scabies mite | In the lab, 5% oil | Mite lifespan shortened | Laboratory only; does not replace treatment |
The dandruff data are the closest to a cosmetic product, but this is a single study. If your scalp is markedly red or flaking, look at the causes of dandruff and see a dermatologist. Treatment of mites and scabies should not be left to home essential oil trials; diagnosis and treatment are for the physician.
Why is oxidised oil riskier?
In tea tree oil, allergy is often attributed not to the fresh oil itself but to the products formed after contact with air. There are two concrete laboratory findings on this:
- In oil left open to air, the peroxide level rose from under 50 ppm to over 500 ppm within 4 days, and p-cymene rose from 2% to 11,5%. Reactions to the oxidised oil also increased.
- Alpha-terpinene acts as the oil's own antioxidant, but at a cost: it quickly breaks down, forming allergenic epoxides and hydrogen peroxide. The sensitising power of the oxidised mixture increases.
In practice this means an open bottle cannot be considered "a bit old but still works". Store it in a small dark bottle with a tight cap, in a cool place. What the ratios mean is explained in the dilution section of the acne article, so we do not repeat it here. For the possibility of allergy, test the new product on the inner arm, twice a day, for 7-10 days.
Why is it being debated in Europe?
Tea tree oil has come to the centre of the regulatory agenda in recent years, and this information changes quickly:
- Classification: The EU's chemical risk committee gave an opinion in 2023 that the oil should be classified as a substance that may damage fertility (category 1B). The basis is animal studies; there are no studies examining this in humans. In November 2025 the European Commission announced a draft including this. The United Kingdom has not, for now, made the same classification mandatory.
- Result in cosmetics: Substances in this class are prohibited in the EU by default, but limited permission can be given if the scientific committee finds them safe. The European consumer safety committee said in October 2025 that the oil is safe in adult products up to 2% in shampoo, 1% in shower gel and face cleanser, and 0,1% in face cream. Sprays and aerosols are outside the scope. It also wrote that the oil is a moderate skin sensitiser and that its stability in the product must be ensured.
- Limit of this page: The final legal text and its application in Turkey may change over time. So the ratios given here are not a legal limit but a scientific opinion.
Who should stay away, and when should you see a doctor?
- Children: The European opinion covers only adult products. Consult your doctor before use on a child. Store the bottle out of reach.
- Pregnancy and breastfeeding: Because of the reproductive toxicity debate and the scarcity of data, do not start on your own; consult your doctor.
- Swallowing: Tea tree oil is not taken orally. If it has been swallowed, seek medical help immediately, without losing time.
- See a dermatologist: If an itchy, blistering rash appears days after application, spreads beyond the area where you applied it, or does not subside within 2 weeks after you stop the oil. 2 weeks is an example; in spreading presentations there is no need to wait. This presentation may be contact dermatitis; a patch test shows which substance you are reacting to.
- Go to the emergency room: If there is swelling of the face or tongue, or breathlessness.
Do not apply pure oil straight to the skin as "natural". For the general risks of volatile oils, see the perfume and essential oils article.
This page is for general information only and does not replace medical diagnosis or treatment. If you have an ongoing skin or scalp problem, consult a dermatologist.