Ten popular essential oils graded, and none earned our top rating

Key takeaways

• Orange scent in a Vienna dentist’s waiting room calmed women in a 72-patient study, but a Dutch study of 219 patients in three larger clinics found no effect on anxiety, mood or pain¹².
• In a 2015 trial of 100 people with pattern hair loss, rosemary oil tied with 2% minoxidil after six months, but it’s one trial, and it hasn’t been repeated in the sources we found⁷.
• Cancer Council Australia says there’s no evidence yet that frankincense oil can treat or prevent cancer in people, and the lab studies didn’t test the oil sold in stores¹³.
• In 1991 the FDA proposed that eugenol, clove oil’s main compound, lacked enough data for toothache relief, a trade newsletter reported; a drugstore label for 85% eugenol drops still lists that unfinished status¹¹¹².
• Swallowed oils can be deadly: the Tennessee Poison Center reports deaths after as little as 4 milliliters of eucalyptus oil and liver injury from clove oil¹⁰.

In 2000, researchers from the University of Vienna’s neurology clinic tried a simple test in a dentist’s waiting room. Some patients waited while an electric dispenser filled the room with the scent of orange. Others waited with no scent¹.

Among the 72 patients, the women who smelled orange reported less anxiety, a better mood and more calm than women who didn’t¹. The study reported those benefits for women only¹.

A decade later, Dutch researchers tried the idea on a bigger stage. In three large dental clinics in Rotterdam, 219 patients waited with orange scent, apple scent or neither².

This time, the scents made no difference to anxiety, mood or pain². The authors suggested that the bustle of a big clinic might have drowned out any calming effect².

Same oil, two answers. That’s a common story in essential oil research. Our lavender articles cover the best-studied oil. Below, we cover the report card for 10 others, from peppermint to frankincense.

Each oil is a different chemical mix, so each needs its own test

An essential oil is a concentrated blend of plant compounds, pressed or steam-distilled from a plant³. Two bottles with the same common name can differ. A single species can come in chemotypes, versions with different chemistry and possibly different effects, and an oil’s makeup shifts as it ages³.

That’s why one oil’s results can’t be borrowed for another. Orange oil is mostly limonene². Clove oil’s key compound is eugenol, and eucalyptus oil’s is eucalyptol¹⁰. They act differently in the body and carry different risks.

The form matters too. A capsule, a skin cream, a diffuser and a drop on a tooth deliver very different doses to very different places. A study of one form tells you little about the others.

Orange and bergamot: calm in some studies, not in others

Sweet orange. The two dental studies above disagree, and a third result adds a twist. In a study NCI describes, people getting stem cell infusions felt less nausea, retching and coughing when they sniffed or tasted fresh orange slices than when they inhaled orange essential oil³.

That doesn’t mean orange oil does nothing. It means the cheapest option, a cut orange, beat the bottle in that study.

Bergamot. In a trial by researchers at Taipei Medical University, published in 2013, 109 patients awaiting outpatient surgery breathed either bergamot oil or plain water vapor⁵. Anxiety scores fell more in the bergamot group⁵. The summary we read didn’t say whether patients or staff were blinded, and it didn’t give the size of the effect⁵.

A trial in children went the other way. In a double-blind study of 37 children and teens getting stem cell infusions, inhaled bergamot didn’t ease nausea, anxiety or pain, and the bergamot group had more nausea⁴.

The sun caution. Citrus oils on the skin before sun exposure can cause phototoxicity, a sunburn-like skin reaction triggered by light⁴. Bergamot is a citrus oil, so keep it off skin that will see the sun.

Rosemary versus minoxidil: one trial, a tie and open questions

Rosemary oil is a popular home remedy for thinning hair. The key human study is a single trial from 2015⁷.

In that trial, published in the dermatology journal SKINmed, 100 people with androgenetic alopecia, the common pattern of hair thinning, applied either rosemary oil or 2% minoxidil, a drugstore hair-regrowth treatment, for six months⁷.

At three months, neither group’s hair count had changed much. By six months, both groups had gained hair, and the difference between them wasn’t significant⁷. Scalp itching rose in both groups but was more common with minoxidil⁷.

That sounds like a win for rosemary, but read the fine print. The abstract we found doesn’t give the rosemary dose or report who paid for the study⁷. Its index terms suggest the volunteers were young men, so the result may not carry over to women⁷. The trial lasted only six months.

The paper has also drawn comments on PubPeer, a website where scientists discuss published research; we couldn’t see what those comments say⁸. Neither the PubPeer page nor the university’s record of the paper shows a retraction or correction⁷⁸.

One small trial is a reason to keep studying rosemary, not proof that it works.

Tea tree and eucalyptus: modest help on the outside, danger on the inside

Tea tree. Aboriginal Australians treated wounds, burns and insect bites with tea tree leaves, and the oil is steam-distilled from those leaves⁹. Today it’s promoted for acne, athlete’s foot, nail fungus and lice⁹.

NCCIH, the federal center for complementary health, updated its review in April 2025⁹. Limited research hints that tea tree oil applied to skin could help acne and athlete’s foot, though for athlete’s foot it may not match standard treatments⁹. For nail fungus, the evidence is too thin to judge⁹.

Oil that’s old, or has sat in heat, light or air, is more likely to irritate skin⁹. Our article on topical plant products covers the acne evidence in more depth.

Eucalyptus. Eucalyptus is often sold in over-the-counter cough remedies⁶. A 2022 review pooled six trials with 1,857 people who had a cough⁶. Eucalyptus products, mostly combinations with other ingredients, beat placebo, with no serious side effects⁶. But the authors called the benefit minimal, with unclear importance for patients⁶.

Never swallow either one. NCCIH says tea tree oil should never be taken by mouth, because it can cause confusion, unsteadiness and coma⁹. The Tennessee Poison Center reports coma after as little as 10 milliliters of tea tree oil, and deaths after as little as 4 milliliters of eucalyptus oil, a bit less than a teaspoon¹⁰.

Clove: a dental standby with an unfinished FDA file

Clove oil’s key compound, eugenol, has long been sold for aching teeth¹¹. In 1978, an FDA advisory panel rated eugenol as safe and effective for toothache, according to a 1992 report in The Pink Sheet, a drug-industry trade newsletter¹¹.

Then, in a 1991 proposal, the FDA moved to put eugenol in a category meaning there wasn’t enough data¹¹. The agency said eugenol can damage living tooth pulp without professional supervision, and it asked for controlled clinical studies¹¹.

One maker, Mentholatum, pushed back, citing eugenol’s long history of use¹¹. Another maker said it couldn’t afford the studies the FDA wanted¹¹.

A drugstore-brand label for 85% eugenol drops, listed since 2015, calls the product a toothache relief agent and gives its FDA marketing category as “OTC monograph not final”¹². One such label tells users to put one or two drops on a cotton pellet in the cavity, see a dentist within 48 hours, and stop after seven days¹².

The bigger danger is swallowing it. The Tennessee Poison Center explains that swallowed eugenol can injure the liver much as an acetaminophen overdose does¹⁰.

Frankincense: the cancer claims come from lab dishes

Frankincense is the fragrant resin of Boswellia trees. Online, the oil is often promoted as a cancer fighter, which is why readers ask cancer groups about it¹³.

Cancer Council Australia looked at that claim and found “no evidence yet that it can treat or prevent cancer in humans”¹³. A handful of lab-dish studies, plus one in mice, reported cancer cells dying or failing to grow¹³.

Look closer, and the gap widens. The council notes that the lab work used preparations from the tree’s gum resin, not the frankincense oil sold in stores, and that the studies varied in species, strength and type of cancer cell¹³.

The human trials that do exist used something else entirely. Experts at Memorial Sloan Kettering Cancer Center describe small trials of boswellia extract taken by mouth, for example in 44 people getting radiation for brain tumors and 75 people with osteoarthritis¹⁴. Their review cites no clinical studies of the essential oil itself, only lab work on its germ-killing effects¹⁴.

Why lab dishes mislead. An oil that kills cells or bacteria in a dish meets them directly, at whatever strength the scientist chooses. In your body, it must get past skin or gut, survive your liver and reach the right tissue at a useful dose. Our article on animal and lab studies explains why so few early results carry over to people.

Ginger, chamomile and peppermint: what scent studies add

Ginger. In a crossover trial NCI describes, women with breast cancer inhaled ginger oil for five days during chemotherapy³. Among 60 who could be evaluated, nausea dropped by a statistically significant amount that was too small to matter clinically, and vomiting barely changed³.

Roman chamomile. In a trial of 103 people with cancer, some got massage with plain carrier oil and others got carrier oil plus Roman chamomile³. Two weeks later, only the chamomile group showed a statistically significant drop in anxiety³. Our chamomile article covers the tea and capsule research and its allergy risks.

Peppermint. Inhaled peppermint did no better than placebo for nausea after surgery in a 2018 Cochrane review of four small studies¹⁵. Our peppermint article covers the stronger evidence for coated capsules in IBS and a forehead rub for tension headache, and our aromatherapy guide covers hospital nausea programs.

The essential oil report card

This is how the 10 oils stack up. “Best human evidence” means trials in people, not lab dishes.

Oil	Uses claimed	Best human evidence	Rating	Main caution
Sweet orange	Anxiety, mood	Calmer women in one 72-person study; no effect in a 219-person study12	Promising but early	Some citrus oils cause sun reactions on skin4
Bergamot	Anxiety, stress	Less presurgery anxiety in 109 patients; more nausea in 37 children45	Promising but early	Sun reaction on skin4
Rosemary	Hair regrowth	Tied with 2% minoxidil in one 100-person trial7	Promising but early	Scalp itching; study has open questions78
Tea tree	Acne, athlete’s foot, nail fungus	A small amount of research for acne and athlete’s foot9	Promising but early	Never swallow; old oil irritates skin9
Eucalyptus	Cough, congestion	Six trials, mostly combination products; tiny benefit6	Promising but early	As little as 4 mL swallowed has killed10
Ginger	Nausea	Chemotherapy nausea fell too little to matter3	Promising but early	Low toxicity when inhaled, NCI says; don’t swallow3
Roman chamomile	Anxiety	One 103-person massage trial3	Promising but early	Skin allergy is possible with any oil used on skin4
Peppermint	Nausea, headache, IBS	Inhaled: no better than placebo for nausea after surgery15	Not enough evidence for nausea after surgery	Covered in our peppermint article
Clove	Toothache	FDA proposed in 1991 that the data were insufficient11	Not enough evidence	Can harm tooth pulp; liver injury if swallowed1011
Frankincense	Cancer, arthritis, skin	None for the oil; lab and mouse studies of resin preparations1314	Not enough evidence	Boswellia extract slowed platelet clumping in lab tests14

No oil reached Strong evidence, our top rating, which requires consistent results from good human trials or reviews. And no use earned Evidence says no, or unsafe across the board, though swallowing tea tree, eucalyptus or clove oil belongs in that category⁹¹⁰.

Using oils with respect, and knowing when to get help

Many of these oils come from deep healing traditions. Tea tree leaves were an Aboriginal Australian remedy⁹, and boswellia has a long history in Ayurveda, India’s traditional medicine, for coughs, asthma and arthritis¹⁴.

Respecting those traditions means treating each oil as the potent, distinct substance it is. Use it for what it was tested for, in the form that was tested, and keep it on the outside of your body unless a clinician says otherwise.

Some safety rules apply to all 10:

• Keep bottles away from children. Oils are thin enough to slip into the lungs, and as little as 2 milliliters breathed in that way can cause chemical pneumonia¹⁰.
• Don’t swallow essential oils. If anyone does, call Poison Help at 1-800-222-1222¹⁰. Call 911 for a seizure, trouble breathing or collapse.
• Watch your skin. Stop at the first rash, and keep citrus oils off skin headed into the sun⁴.
• Don’t swap an oil for care that works. A toothache needs a dentist¹², and cancer needs proven treatment¹³.

Questions readers ask

The bottom line

Essential oils aren’t interchangeable. Each one is a distinct chemical mix, and the research has to be read oil by oil, use by use. None of the 10 popular oils we graded has strong evidence, and several of the most popular claims, like frankincense for cancer, rest on lab dishes rather than people.

A few oils have earned a closer look for narrow uses: tea tree on the skin, eucalyptus for cough, rosemary for thinning hair. Enjoy oils for scent and comfort, use them on the outside, keep them away from children, and bring real health problems to a clinician.

Keep exploring: how aromatherapy works.

Related reading

• Hospitals offer aromatherapy for nausea, and the best-supported sniff isn’t an oil
• Lavender can mean several plants, and beyond anxiety capsules the evidence is thin
• Peppermint oil has the trials, but the tea most people drink doesn’t
• Only 1 in 20 treatments tested in animals wins approval for people
• Who paid for the study matters, even when the science is real

Sources

1. Lehrner J, Eckersberger C, Walla P, Pötsch G, Deecke L. “Ambient Odor of Orange in a Dental Office Reduces Anxiety and Improves Mood in Female Patients.” Physiology & Behavior, 2000;71(1-2):83-86 (bibliographic record). pubmed.ncbi.nlm.nih.gov
2. Toet A, Smeets MAM, van Dijk E, et al. “Effects of Pleasant Ambient Fragrances on Dental Fear: Comparing Apples and Oranges.” Chemosensory Perception, 2010;3:182-189. link.springer.com
3. National Cancer Institute. “Aromatherapy With Essential Oils (PDQ)–Health Professional Version.” NCI, updated October 31, 2024. cancer.gov
4. National Cancer Institute. “Aromatherapy and Essential Oils (PDQ)–Health Professional Version.” 2016 version, NCBI Bookshelf.
5. Ni CH, Hou WH, Kao CC, et al. “The Anxiolytic Effect of Aromatherapy on Patients Awaiting Ambulatory Surgery: A Randomized Controlled Trial.” Evidence-Based Complementary and Alternative Medicine, 2013:927419 (Taipei Medical University record). hub.tmu.edu.tw
6. Her L, Kanjanasilp J, Chaiyakunapruk N, Sawangjit R. “Efficacy and Safety of Eucalyptus for Relieving Cough: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.” Journal of Integrative and Complementary Medicine, 2022;28(3):218-226. pubmed.ncbi.nlm.nih.gov
7. Panahi Y, Taghizadeh M, Tahmasbpour Marzony E, Sahebkar A. “Rosemary Oil vs Minoxidil 2% for the Treatment of Androgenetic Alopecia: A Randomized Comparative Trial.” SKINmed, 2015;13(1):15-21 (Baqiyatallah University repository abstract). pubmed.ncbi.nlm.nih.gov
8. PubPeer. Discussion page for Panahi Y, et al., SKINmed 2015 (PMID 25842469). Accessed October 2026. pubpeer.com
9. National Center for Complementary and Integrative Health. “Tea Tree Oil.” NIH, last updated April 2025. nccih.nih.gov
10. Loden J. “What Are the Commonly Used but Potentially Toxic Essential Oils?” Tennessee Poison Center, Vanderbilt University Medical Center, May 3, 2016. vumc.org
11. The Pink Sheet. “Eugenol for Toothache Pain Should Retain Category I Status.” March 23, 1992 (on FDA’s September 24, 1991 tentative final monograph for OTC oral health care products). insights.citeline.com
12. Walgreens Natural Eugenol Toothache Medication, drug facts label (eugenol 85%; marketing category “OTC monograph not final”). OTCLabels.com, accessed October 2026. otclabels.com
13. Cancer Council Australia. “Does Frankincense Oil Have Cancer-Fighting Properties?” iHeard, last modified October 14, 2026. cancer.org.au
14. Deng G, Gubili J. “Boswellia.” The ASCO Post, Integrative Oncology series (Memorial Sloan Kettering Cancer Center), November 25, 2019. ascopost.com
15. Hines S, Steels E, Chang A, Gibbons K. “Aromatherapy for Treatment of Postoperative Nausea and Vomiting.” Cochrane Database of Systematic Reviews, 2018, Issue 3, CD007598.pub3. cochranelibrary.com