Tea tree oil has become a fixture in medicine cabinets and bathroom shelves around the world. You’ll find it in shampoos, face washes, wound care products, and household cleaners. The claims surrounding it range from reasonable (it kills some bacteria) to absurd (it cures everything). So what does the evidence actually show?

I’ve gone through the clinical research on tea tree oil to separate what’s reasonably well-supported from what’s mostly marketing. The findings are interesting but inconsistent, and the quality of many studies leaves something to be desired.

What is tea tree oil?

Tea tree oil is an essential oil steam-distilled from the leaves and terminal branches of Melaleuca alternifolia, a tree native to the coastal regions of northern New South Wales and southern Queensland in Australia. The Bundjalung Aboriginal people have used the crushed leaves medicinally for generations, though commercial production of the distilled oil began relatively recently in the 1920s.

The oil has a pale yellow colour with a fresh, camphor-like smell. Its primary active components are terpinen-4-ol (which typically makes up 30-40% of the oil), γ-terpinene, and α-terpinene. The antimicrobial activity appears to come mainly from the terpinen-4-ol content, which is why quality standards specify minimum concentrations of this compound 1.

During World War II, tea tree oil was included in Australian military first aid kits for treating skin infections and wounds. Production actually stopped during the war because the workers harvesting the leaves were conscripted, and the industry didn’t recover until the 1970s when interest in natural remedies revived.

Laboratory studies have demonstrated that tea tree oil has antibacterial, antifungal, and antiviral properties. However, and this is important, what kills microorganisms in a petri dish doesn’t always work as well on human skin or mucous membranes. The jump from lab studies to clinical effectiveness is often where natural remedies fail to deliver on their promise.

What does the research show about tea tree oil?

1. Oral health: plaque and gingivitis

Periodontal disease affects a significant portion of the global population and increases the risk of cardiovascular problems, particularly in older adults 2. Researchers have explored various natural products as additions to standard oral hygiene.

A double-blind study involving 152 school-age children compared mouthwashes containing tea tree oil, aloe vera, or chlorhexidine against a placebo over six weeks. All three active mouthwashes reduced plaque index, gum inflammation, and counts of Streptococcus mutans (a bacterium strongly associated with tooth decay) compared to placebo.

My take: The results are promising, but chlorhexidine is already an established antiseptic mouthwash. The interesting question is whether tea tree oil offers any advantage over existing products, and this study doesn’t really answer that. The tea tree oil performed similarly to chlorhexidine, which at least suggests it’s doing something genuinely antimicrobial rather than just tasting unpleasant enough to encourage more thorough brushing.

2. Rosacea

Rosacea is a chronic inflammatory skin condition causing facial redness, visible blood vessels, and sometimes acne-like pustules. It affects somewhere between 5% and 18% of the population depending on which country you’re looking at, with people of Northern European ancestry being most commonly affected.

One theory suggests that Demodex mites (microscopic creatures that live in hair follicles) may play a role in rosacea. Tea tree oil has documented acaricidal (mite-killing) properties, which led researchers to test it for this condition.

A double-blind trial involving 47 rosacea patients found that a topical gel combining tea tree oil with permethrin (an antiparasitic) reduced mite density and improved clinical symptoms including papules, pustules, redness, burning, and tingling compared to placebo 3.

The catch: This was a combination treatment, so we can’t attribute the benefits specifically to tea tree oil. Also, 47 participants is a small sample. I’d want to see larger studies testing tea tree oil alone before drawing firm conclusions.

3. Mild hirsutism (excess hair growth)

Hirsutism, the growth of coarse hair in areas where women typically don’t have it, affects 5-10% of women of childbearing age. Beyond the physical appearance, it can cause considerable psychological distress.

A small study of 24 women with mild idiopathic hirsutism (meaning no identified hormonal cause) found that a topical spray containing lavender and tea tree essential oils reduced total hirsutism scores and hair shaft diameter over three months 4.

Worth noting: Twenty-four participants is extremely small for drawing meaningful conclusions, and the spray combined two oils, making it impossible to know which was responsible for any effect. The mechanism proposed involves possible anti-androgenic activity, but this is speculative. I wouldn’t bet the farm on this one, though it’s intriguing enough to warrant further investigation.

4. Nail fungus (onychomycosis)

Fungal nail infections are common, especially in older adults and people with diabetes or compromised immune systems. They’re notoriously difficult to treat, with oral antifungal medications being the most effective but carrying risks of liver toxicity.

An older double-blind study from 1994 involving 117 patients with distal onychomycosis compared 1% clotrimazole solution (a standard antifungal) to 100% tea tree oil applied twice daily for six months. Both treatments produced similar improvements in nail appearance and symptoms, with about 60% of patients in each group showing full or partial clearing 5.

Reality check: Matching the performance of an existing antifungal is actually meaningful. However, 60% partial clearing isn’t exactly a cure, and six months is a long time to apply oil twice daily. The study didn’t include a placebo group, so we don’t know how many patients might have improved anyway. Nail fungus isn’t going anywhere quickly regardless of treatment, which makes it hard to assess whether interventions are actually working.

5. Acne

Acne affects roughly 85% of adolescents and young adults, and even mild cases can significantly impact self-esteem and quality of life. The condition involves blocked hair follicles, excess sebum production, and bacterial colonisation, particularly by Cutibacterium acnes.

A double-blind study of 60 patients with mild to moderate acne compared 5% tea tree oil gel to placebo over 45 days. The tea tree oil group showed significantly greater reductions in total acne lesion counts and acne severity index scores, with improvement roughly 3.5 to 5.7 times greater than placebo 6.

Another study compared 5% tea tree oil gel to 5% benzoyl peroxide lotion (a standard acne treatment). Both reduced acne lesions, though benzoyl peroxide worked faster. The tea tree oil caused fewer side effects like dryness, stinging, and peeling 7.

My assessment: This is probably the best-supported use of tea tree oil. Multiple studies show consistent effects, and the mechanism makes sense given tea tree oil’s antibacterial properties. That said, 5% tea tree oil won’t work as quickly as benzoyl peroxide or prescription treatments. For mild acne, it might be worth trying. For moderate to severe cases, I’d stick with proven treatments.

6. Athlete’s foot (tinea pedis)

Athlete’s foot is a fungal infection that causes itching, scaling, and sometimes painful cracking between the toes. It’s extremely common and tends to recur because the fungi thrive in warm, moist environments.

A double-blind study of 158 patients with tinea pedis tested 25% and 50% tea tree oil solutions against placebo over four weeks. The mycological cure rates (meaning the fungus was actually eliminated, not just that symptoms improved) were 55% for 25% tea tree oil and 64% for 50% tea tree oil, compared to 31% for placebo 8.

The problem: Four patients withdrew due to dermatitis, which suggests that concentrated tea tree oil can irritate some people’s skin. The cure rates, while better than placebo, aren’t dramatically impressive either. Standard antifungal creams typically achieve higher cure rates with fewer side effects.

7. Dandruff and seborrhoeic dermatitis

Dandruff is essentially a mild, non-inflammatory form of seborrhoeic dermatitis limited to the scalp. It involves excessive scalp flaking, often with itching, and affects roughly half of adults at some point.

A controlled study of 126 people with mild to moderate dandruff found that using a 5% tea tree oil shampoo daily for four weeks reduced scalp lesion scores by 40%, compared to 11% with placebo shampoo. Self-reported itchiness and greasiness also improved 9.

In practice: This is a reasonable use case. Dandruff isn’t serious, the treatment (shampoo) is easy to use, and the risks are minimal. If regular dandruff shampoos aren’t working for you, a tea tree oil formulation might be worth trying. Don’t expect miracles, but a 40% improvement isn’t nothing.

8. Scabies

Scabies is caused by a tiny mite that burrows into the skin, causing intense itching and a characteristic rash. It’s particularly prevalent in crowded living conditions and can lead to serious secondary bacterial infections.

Laboratory studies show tea tree oil has acaricidal activity against scabies mites, and its anti-inflammatory properties could theoretically help with the immune response to mite antigens 10. Case reports describe successful treatment of crusted scabies (a severe form) with tea tree oil when standard treatments failed.

A word of caution: This is where the evidence gets thin. While the lab studies are promising, there are no large clinical trials testing tea tree oil for scabies. Standard treatments (permethrin cream or oral ivermectin) remain the first-line approach. I wouldn’t recommend experimenting with tea tree oil for scabies when proven treatments exist, especially given the risk of spreading the infection while trying unproven alternatives.

Side effects of tea tree oil

Topical tea tree oil at appropriate concentrations (typically 5-10%) is generally well tolerated. However, side effects can occur, particularly with higher concentrations or sensitive skin:

Skin irritation: itching, burning, redness, and dryness are the most common complaints
Allergic contact dermatitis: some people develop true allergic reactions to tea tree oil components
Photosensitivity: there’s limited evidence that tea tree oil might increase sun sensitivity

The NHS notes that skin irritation is the most commonly reported issue, and recommends patch testing before widespread use 11.

Safety precautions (9 contraindications)

Never swallow tea tree oil. Oral ingestion has caused serious adverse effects including confusion, drowsiness, hallucinations, loss of coordination, diarrhoea, vomiting, and in severe cases, coma. Even small amounts can be toxic 12.
Be cautious with eucalyptol sensitivity. Some tea tree oil products contain eucalyptol, which can trigger reactions in sensitive individuals.
Don’t use oxidised oil. Tea tree oil degrades when exposed to air, light, and heat. Oxidised oil contains higher levels of irritating compounds. Use within a year of opening and store in a dark, cool place.
Store properly. Keep the bottle tightly sealed, away from direct sunlight and heat.
Dilute before applying. Using undiluted tea tree oil directly on skin frequently causes irritation. Mix with a carrier oil such as olive oil, coconut oil, or sweet almond oil before application.
Avoid sensitive areas. Don’t apply near eyes, inside the nose, on mucous membranes, or on broken skin without medical guidance.
Exercise caution in pregnancy and breastfeeding. The safety of topical tea tree oil during pregnancy and lactation hasn’t been established. While occasional use is probably fine, there’s insufficient evidence to make definitive recommendations.
Keep away from pets. Tea tree oil is toxic to cats and dogs, whether ingested or absorbed through the skin. Symptoms of poisoning include muscle tremors, weakness, difficulty walking, low body temperature, and excessive drooling. The ASPCA lists it as toxic to companion animals.
Be aware of potential hormonal effects in children. A case series published in the New England Journal of Medicine reported prepubertal gynaecomastia (breast enlargement) in boys who used products containing tea tree oil or lavender oil. The condition resolved when the products were discontinued 13. While the evidence is limited to case reports rather than controlled studies, caution in prepubertal children seems reasonable.

Practical considerations

If you’re thinking about using tea tree oil, here are some things worth considering:

Quality matters. Look for products that specify the terpinen-4-ol content (should be at least 30%) and low cineole content (preferably under 15%). The International Organisation for Standardisation (ISO) has set standards for tea tree oil quality.

Concentration matters. Most clinical studies used 5% tea tree oil for skin conditions. Higher concentrations don’t necessarily work better and do increase the risk of irritation.

Patience is required. Natural remedies generally work more slowly than pharmaceutical options. If you’re trying tea tree oil for acne or dandruff, give it at least four to six weeks before deciding whether it’s working.

It’s not a replacement for medical care. Tea tree oil might be helpful for minor skin conditions, but serious infections, persistent problems, or conditions that aren’t improving need proper medical evaluation. Recurrent UTIs, for instance, require medical treatment rather than home remedies.

The evidence for tea tree oil is genuinely mixed. For some conditions, particularly mild acne and dandruff, it appears to be a reasonable option with a plausible mechanism and acceptable safety profile. For others, the evidence is too thin or the condition too serious to recommend it as a first-line treatment. As with most natural remedies, the truth sits somewhere between the enthusiasts who think it cures everything and the sceptics who dismiss it entirely.