Melaleuca Alternifolia (Tea Tree) Leaf Oil

What it is

Tea tree oil is steam-distilled from the leaves of Melaleuca alternifolia, a shrub native to New South Wales. Its main active component is terpinen-4-ol, typically 30 to 48%, and its composition is defined by the international standard ISO 4730. It appears in clay masks and spot treatments aimed at oily and blemish-prone skin because of genuine antibacterial and anti-inflammatory activity.

What it does well

• Reduces inflammatory acne lesions

  Small randomised trials of 5% tea tree oil gel show reductions in inflamed lesion counts, slower in onset than benzoyl peroxide but with less dryness and peeling. Evidence quality is modest and trial sizes are small.

  Moderate evidence

• Has broad antibacterial and antifungal activity

  Terpinen-4-ol is active in vitro against Cutibacterium acnes, Staphylococcus aureus and several dermatophytes. This laboratory activity is well established, though it does not automatically translate into clinical results at the low levels used in a typical mask.

  Strong evidence

• Assessed as safe by the SCCS at defined concentrations

  In its 2025 opinion the SCCS considered tea tree oil safe for adults in non-spray products at up to 2% in shampoo, 1% in shower gel and face wash, and 0.1% in face cream, provided the composition meets ISO 4730:2017.

  Moderate evidence

Worth knowing

• A documented contact allergen, more so as it ages

  Routine patch testing finds positive reactions in roughly 0.1 to 3.5% of dermatitis patients depending on the population. An Australian series of 2320 patients found 41 positives to oxidised tea tree oil, a prevalence of 1.8%, with clinical relevance in 41% of those cases.

  Matters most toPeople with eczema, sensitive skin, or who use undiluted tea tree oil directly on spots.

• Oxidation makes it substantially more sensitising

  Fresh tea tree oil is a weak to moderate sensitiser. Light, heat and air convert it into ascaridole, p-cymene hydroperoxides and other degradation products that are considerably more allergenic. The SCCS specifically flagged the lack of stability data and required composition to stay within ISO limits through shelf life.

  Matters most toAnyone using an old bottle of neat oil or a long-opened product.

• Undiluted use on the face is a bad idea

  Neat tea tree oil applied directly to skin causes irritant reactions and is the most common route to sensitisation. It is also toxic if swallowed, which matters for households with young children.

  Matters most toPeople self-treating acne with neat oil, and parents of small children.

• The claim that it causes breast growth in boys is not established

  A small number of case reports linked topical tea tree and lavender oils to prepubertal gynaecomastia, but the evidence is weak, uncontrolled and has not been reproduced in controlled studies. It is worth knowing about, but it is not a demonstrated effect at cosmetic exposure levels.

  Matters most toParents who have seen this claim circulated online.

Where the EU stands

Sources (3)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Tea tree oil: contact allergy and chemical composition

   Contact Dermatitis · 2016 · doi:10.1111/cod.12591

   A systematic review concluding that positive patch test rates in routine testing range from 0.1% to 3.5%, and that fresh tea tree oil is a weak to moderate sensitiser whose potency rises sharply on oxidation.

2. [2]
   Allergy to tea tree oil: retrospective review of 41 cases with positive patch tests over 4.5 years

   Australasian Journal of Dermatology · 2007 · doi:10.1111/j.1440-0960.2007.00341.x

   Among 2320 patch-tested Australian patients, 1.8% reacted to oxidised tea tree oil, and the reaction was judged clinically relevant in 41% of those cases.

3. [3]
   Scientific Opinion on Tea Tree Oil (CAS/EC No. 68647-73-4 / 285-377-1) (SCCS/1681/25)

   SCCS - Scientific Committee on Consumer Safety, European Commission · 2025

   The SCCS considered tea tree oil safe for adults in non-spray cosmetics at up to 2% in shampoo, 1% in shower gel and face wash and 0.1% in face cream, while classifying it as a moderate skin sensitiser and flagging missing stability data.