The quick answer
Tea tree oil is an essential oil steam-distilled from the leaves of Melaleuca alternifolia, an Australian tree, and its main active compound is terpinen-4-ol. Small trials suggest that, used on the skin, it helps mild to moderate acne (a 5% gel), athlete's foot and dandruff (a 5% shampoo), with weaker evidence for toenail fungus. It is for external use only: it is toxic if swallowed, it should be diluted for most uses, and it is dangerous for cats and dogs.
Never swallow tea tree oil. NCCIH warns that taking it by mouth can cause confusion, loss of balance and coma. Keep it away from pets and out of children's reach.
What is tea tree oil?
Tea tree oil (in Polish, olejek herbaciany or olejek z drzewa herbacianego) comes from Melaleuca alternifolia, a tree native to New South Wales and Queensland. The leaves are steam-distilled to make the oil. Most of the world's supply is still produced in Australia, with smaller amounts from China and several African countries (NCCIH). Aboriginal Australians traditionally used the leaves for wounds, burns and insect bites.
The oil's main active compound is terpinen-4-ol. An international standard, ISO 4730, sets the expected chemical profile for tea tree oil. In the version described in a widely cited 2006 review, it called for at least 30% terpinen-4-ol and no more than 15% 1,8-cineole, a compound that tends to run lower when terpinen-4-ol runs higher (Carson et al., Clinical Microbiology Reviews, 2006). Lab studies show the oil kills a wide range of bacteria and fungi, which is the basis for most of its uses.
Tea tree oil uses: what the evidence shows
NCCIH sums it up this way: a small amount of evidence suggests topical tea tree oil may help acne and athlete's foot, and for most other uses there isn't enough evidence to say. A 2023 review of 46 randomized trials rated the overall research quality poor to modest (Kairey et al., Frontiers in Pharmacology, 2023). The most cited trials:
| Use | Concentration studied | What happened |
|---|---|---|
| Mild to moderate acne | 5% gel | In 124 people, both it and 5% benzoyl peroxide reduced inflamed and non-inflamed spots; tea tree worked more slowly but caused fewer side effects (Bassett et al., 1990) |
| Athlete's foot (between the toes) | 25% and 50% solution | Marked improvement in 68 to 72% of users vs. 39% on placebo after four weeks; fungal cure in 64% at 50% strength vs. 31% (Satchell et al., 2002) |
| Dandruff | 5% shampoo | 41% improvement in severity score vs. 11% on placebo after four weeks, with no side effects reported (Satchell et al., 2002) |
| Toenail fungus | 100% oil | After six months, results were similar to 1% clotrimazole, with about 60% partly or fully improved, but culture cure was low (18%) (Buck et al., 1994) |
| Dental plaque | 0.2% to 0.5% mouthwash, spat out | May limit plaque buildup; evidence still limited (Kairey et al., 2023) |
Two cautions on that table. First, these are single, fairly small studies. Second, the higher concentrations came with more skin reactions: in the athlete's foot trial, about 4% of people using the oil developed moderate to severe dermatitis, and the 2023 review found side effects were generally minor except at strengths of 25% or more.
How to dilute tea tree oil
For most skin uses, dilute tea tree oil before applying it. The acne and dandruff studies used 5%. That works out to 1 part tea tree oil in 20 parts total, for example 1 mL of tea tree oil mixed into 19 mL of a carrier oil, gel or unscented shampoo.
- Pick a carrier. A plain, unscented oil works for skin; an unscented shampoo works for the scalp. For more on plant oils, see our herbal oils guide.
- Patch test first. Put a little of your mix on the inner arm and wait a day. Redness, itching or swelling means stop.
- Keep it away from eyes and mouth.
Tea tree oil safety
Old oil is more allergenic. Tea tree oil has caused more published allergic reactions than any other essential oil, and most came from using the pure oil. Fresh oil is a weak to moderate allergen, but oxidation makes it more potent (de Groot and Schmidt, Contact Dermatitis, 2016). Light, heat, air and moisture all change the oil over time, so store it in a dark, tightly closed bottle in a cool, dry place (Carson et al., 2006). NCCIH notes that skin reactions are more likely with old products or ones exposed to heat, light or air.
Toxic if swallowed. Taking tea tree oil by mouth has caused confusion, unsteadiness, inability to walk and coma (NCCIH). Mouthwashes that contain it should be spat out.
Dangerous for pets. A review of 443 cases reported to the ASPCA Animal Poison Control Center found that 100% tea tree oil, usually applied on purpose by owners, made dogs and cats drool, become lethargic, wobbly or weak in the legs, and tremble, starting within 2 to 12 hours and lasting up to three days. Young, small cats were at greatest risk (Khan et al., JAVMA, 2014). Don't use it on pets.
Breast growth in boys (debated). In 2007, researchers described three boys who developed breast tissue while using products containing lavender and tea tree oils; it went away after the products were stopped, and the oils showed weak hormone-like activity in lab cells (Henley et al., New England Journal of Medicine, 2007). MSKCC notes that the hormone link has been challenged and needs confirmation. If you have a young son, it's reasonable to ask his pediatrician before using these oils on him regularly.
Pregnancy. NCCIH says topical tea tree oil products may be safe during pregnancy and breastfeeding. Swallowing it is never safe.
How to choose a tea tree oil (any brand)
Many brands sell tea tree oil, including the big names people search for by brand. Whatever the brand, the label should tell you the same few things:
- The Latin name Melaleuca alternifolia, so you know it is true tea tree and not another plant.
- Whether it is 100% oil or already diluted.
- Ideally, a statement that it meets ISO 4730 or a terpinen-4-ol percentage.
- A dark glass bottle and a date or lot number, since freshness matters for allergy risk.
- Clear "for external use only" directions.
Find it at William's
- Now tea tree oil, 1 oz: pure Melaleuca alternifolia oil, steam-distilled from leaves and twigs.
- Now organic tea tree oil, 1 oz: the same oil from certified organic plants.
- Desert Essence tea tree oil (100% Australian), 1 oz: pure tea tree oil sourced from Australian plantations.
- Tea Tree Therapy pure tea tree oil, 1 oz: 100% Australian tea tree oil.
All four are full-strength oils, so plan to dilute them. If you're looking for other skin-care oils, see our guides to neem oil and eucalyptus.
Frequently Asked Questions
Can I put tea tree oil directly on a pimple?
It's better to dilute it. The acne trial that found a benefit used a 5% gel, and pure oil is more likely to cause irritation and allergy. Apply a diluted mix to the spot and stop if your skin gets red or itchy.
What is tea tree oil used for?
People use it on the skin for acne, athlete's foot, toenail fungus, dandruff and minor skin problems. The best, though still limited, evidence is for acne and athlete's foot. It is not meant to be swallowed.
Does tea tree oil go bad?
Yes. Exposure to light, heat and air changes its chemistry, and oxidized oil is more likely to cause allergic skin reactions. Keep the cap tight, store it somewhere cool and dark, and replace oil that smells different or has been open a long time.
Is tea tree oil safe for dogs and cats?
No. Veterinary poison control data show that 100% tea tree oil on the skin or swallowed can cause drooling, weakness, wobbliness and tremors in dogs and cats, sometimes for days. Small young cats are most at risk.
Does tea tree oil help toenail fungus?
Maybe a little. In one trial, twice-daily 100% oil for six months improved nail appearance in about 60% of people, similar to a clotrimazole solution, but only 18% were cured on culture. NCCIH says the evidence is too limited to draw conclusions.
Shop it at William’s
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Now
Now TEA TREE OIL 1 OZ
$8.99
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Desert Essence
Desert Essence 100% AUSTRALIAN TEA TREE OIL 1 Oil
$13.29
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Tea Tree Therapy
TEA TREE THERAPY, INC. PURE TEA OIL 1OZ
$14.62
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Now
Now ORGANIC TEA TREE OIL 1 OZ
$13.99
Online prices can differ from in-store prices. Call ahead to check stock.