Efficacy and safety of Melaleuca alternifolia (tea tree) oil for human health—A systematic review of randomized controlled trials
Frontiers in Pharmacology · 6 authors, 2 centres
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This systematic review of 46 RCTs found that tea tree oil shows potential efficacy for acne, dandruff, tinea pedis, Demodex blepharitis, and oral hygiene, but evidence is limited by poor study quality and lack of standardized formulations. Tea tree oil was less effective than standard treatments like benzoyl peroxide for acne and chlorhexidine for plaque control, and adverse effects included skin irritation and burning. The review highlights the need for rigorous future trials with standardized tea tree oil products and adequate safety reporting.
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**Background:** Tea tree oil (TTO), the essential oil derived from *Melaleuca alternifolia*, has a long history of traditional use by First Nations Australians for wounds, burns, and infections. It possesses antimicrobial, anti-inflammatory, and analgesic properties. Despite established traditional use and *in vitro* data, comprehensive evidence from human randomized controlled trials (RCTs) is lacking. This systematic review aimed to critically appraise RCTs testing the therapeutic efficacy and/or safety of TTO on any human health outcome.
**Methods:** The review protocol was prospectively registered (PROSPERO CRD42021285168). Electronic databases PubMed, Scopus, and CENTRAL were searched on 12 August 2022. RCTs testing TTO from *M. alternifolia* on any health-related outcome in humans were included. Interventions using TTO combined with other active ingredients were excluded. Risk of bias was assessed using the Cochrane RoB 1.0 tool. Data were extracted and verified by two authors.
**Key Results:** 46 RCTs were included, spanning dentistry (n=18), dermatology (n=9), infectious disease (n=9), ophthalmology (n=6), podiatry (n=3), and one on anxiety/sleep. In dentistry, 0.2%–0.5% TTO mouthwashes reduced plaque and gingivitis compared to placebo (e.g., Kamath et al. 2020: plaque index reduction p<0.001 vs placebo), but were generally less effective than chlorhexidine. A 5% TTO gel as adjunct to scaling and root planing improved periodontal outcomes (e.g., Taalab et al. 2021: clinical attachment level significantly lower at 6 months, p=0.004). In dermatology, 5% TTO gel reduced acne lesions vs placebo (Enshaieh et al. 2007: 43.6% vs 12.0% reduction, p<0.001), but was less effective than benzoyl peroxide for inflamed lesions. A 5% TTO shampoo reduced dandruff severity (Satchell et al. 2002a: −41.2% vs −11.2%, p<0.001). In infectious disease, a 10% TTO hand disinfectant showed greater microbial reduction than alcohol-based sanitizer (Youn et al. 2021: log reduction −5.50 vs −2.33, p<0.05). TTO regimens for MRSA decolonization showed mixed results; one trial found 10% TTO in paraffin oil significantly reduced wound MRSA counts (Lee et al. 2014: 93 vs 10312 CFU/mL at week 4, p≤0.001). In ophthalmology, TTO eyelid wipes reduced Demodex mite counts (Wong et al. 2019: median 0 vs 2, p=0.04). In podiatry, 25%–50% TTO improved tinea pedis mycological cure vs placebo (Satchell et al. 2002b: 23/36 and 18/33 vs 14/45, p<0.01). Adverse effects included skin irritation, burning, and dermatitis, especially with higher concentrations. Many studies had unclear or high risk of bias, particularly regarding blinding and incomplete reporting.
**Clinical Implications:** TTO shows promise for several dermatological, oral, and ophthalmic conditions, but current evidence is insufficient to recommend it as a first-line therapy over standard treatments. The quality of evidence is limited by small sample sizes, lack of standardized TTO formulations, and inadequate safety reporting. Future RCTs should use chemically characterized TTO, include appropriate controls, assess compliance and adverse events systematically, and compare TTO to standard care. Clinicians should be aware of potential skin irritation and the risk of allergic reactions, especially with oxidized or adulterated products.