Eucalyptus

Eucalyptus globulus Labill. belongs to Myrtaceae, the myrtle family, which the Australian National Botanic Gardens (ANBG) describes as widespread in Australia and tropical America. The genus Eucalyptus has about 800 species, almost all Australian, with a few on islands to the north. The ANBG records that the French botanist Jacques-Julien Houtou de Labillardière first collected the blue gum on the south-east coast of Tasmania in 1792–93, while sailing with an expedition sent to search for the missing navigator La Pérouse. The genus name comes from the Greek eu, well, and kalypto, to cover as with a lid, after the cap-like operculum that protects the stamens in the bud and falls as the flower opens; globulus, ball-like, refers to the fruit. Several subspecies are recognized. The typical one, subsp. globulus, grows in tall open forest in south-eastern Tasmania and along its east coast, on King and Flinders Islands in Bass Strait, and on the mainland only at Wilson’s Promontory and Cape Otway in southern Victoria. It was proclaimed Tasmania’s floral emblem on 27 November 1962. The tree is now planted in many parts of the world, and EMA’s assessment names the coasts of Spain, the Black Sea, and the Caucasus as the main producing regions for the medicinal leaf.

Under good conditions the Tasmanian blue gum is a tall, straight tree up to 70 meters high, with a trunk 2 meters across (ANBG). Rough, deeply furrowed gray bark persists at the base, but higher up it is shed in strips, leaving the branches and most of the trunk smooth. The tree carries two strikingly different kinds of leaves. Young shoots bear broad juvenile leaves, about 6–15 cm long, in opposite pairs on square stems and coated with a blue-gray waxy bloom, which is the origin of the name blue gum; florists prize them as backing foliage. Adult leaves are narrow, sickle-shaped, and dark glossy green, arranged alternately on rounded stems, and 15–35 cm long. EMA’s assessment describes the leathery leaves as studded with colorless glands containing the fragrant volatile oil. The buds are top-shaped, ribbed, and warty, with a flattened lid bearing a central knob. Cream flowers sit singly where leaf meets stem and produce copious nectar that tends to yield a strongly flavored honey. They ripen into woody fruits 1.5–2.5 cm across, which release numerous small seeds through valves on top.

The medicinal leaf, Eucalypti folium, is defined in the European Pharmacopoeia as the whole or cut dried leaves of older branches of E. globulus, containing at least 20 ml of essential oil per kilogram (15 ml for cut leaf). EMA’s assessment puts the oil content of dried leaves at 1–3.5% and the cineole share of that oil at 54–95%, alongside smaller amounts of pinenes, cymene, and other monoterpenes; flavonoids such as rutin, hyperoside, and quercitrin; gallotannins; and unusual compounds called euglobals and macrocarpals. Younger leaves tend to hold more oil, while adult leaves have a higher proportion of cineole. Eucalyptus oil, Eucalypti aetheroleum, is a separate product: the pharmacopoeia defines it as oil obtained by steam distillation and rectification from the fresh leaves or terminal branchlets of cineole-rich species, mainly E. globulus, E. polybractea, and E. smithii, with at least 70% 1,8-cineole and no more than 0.1% camphor. Some species, such as E. polybractea and E. kochii, yield oils with 80–95% cineole. Not every “eucalyptus” product comes from these trees: the insect repellent sold as oil of lemon eucalyptus is made from the lemon-scented gum, now classified as Corymbia citriodora, and its active ingredient is a different compound, PMD (para-menthane-3,8-diol).

Eucalypts were medicine in Australia long before they were a European export. EMA’s assessment report notes that Aboriginal Australians already made use of the medicinal benefits of eucalyptus. The first Europeans to distill the oil were colonial surgeons: the Australian Dictionary of Biography credits John White, Dennis Considen, and Robert Officer with distilling eucalyptus oil well before 1853. Even so, the oil was slow to reach European pharmacy. EMA, citing a 1946 review by Boyd and Pearson, says that little or no reference to eucalyptus oil can be found in books on materia medica published before the second half of the nineteenth century, and it names Köhler’s monograph of 1873 as one of the first European summaries of the plant, its preparations, and their efficacy and safety. Köhler described eucalyptus preparations used in southern Europe for fever, nerve pain, asthma, lung tuberculosis, and as antiseptics, a list that reflects the era’s hopes for the tree more than any tested effect. Later European pharmacopoeias defined the medicinal leaf by its minimum oil content, as EMA’s assessment shows.

The industry that made eucalyptus oil a household name began in colonial Victoria. Joseph Bosisto, a pharmacist born in Leeds in 1824, sailed for Adelaide in 1848 and became a lifelong friend of the botanist Ferdinand Mueller. After settling in Richmond, Victoria, he ran a busy pharmacy where people consulted him as “Doctor” Bosisto, and his first stills were near Dandenong, though his search for suitable leaves took him far afield. According to the Australian Dictionary of Biography, he was not the first to distill eucalyptus oil but was probably the first to make it commercially, winning repute for manufacturing Australia’s first “original” product, sold under a famous parrot trademark on a yellow label. His products were known in Britain by 1865 and later in Europe, India, and South Africa. Bosisto, a founder of the Pharmaceutical Society of Victoria in 1857, wrote with enthusiasm about the eucalypt as a “Fever Destroying Tree” whose influence could defeat even virulent fever. Today’s regulatory monographs make no such claim; they recognize eucalyptus only for cough with a cold and, for the oil, muscle pain.

In twentieth-century Europe eucalyptus became a mainstay of cough and cold remedies. EMA quotes Madaus (1938) describing a syrup for whooping cough, inhalations for catarrh, inflammatory airway disease, and asthma, uses for fever, influenza, rheumatism, neuralgia, malaria, and bleeding gums, and external use of the leaves as an antiseptic. The French Pharmacopoeia of 1976 called eucalyptus an antiseptic for the lung complications of influenza. German Commission E monographs on the leaf and, in 1986, on the oil, followed by ESCOP and WHO monographs, framed eucalyptus around catarrh of the airways, with the oil also rubbed on for rheumatic complaints. Use remained widespread. In a German survey of parents conducted in 2007, 43.9% of children had been given eucalyptus preparations in the previous six years, and in an older survey of 100 adults in Oregon, 39% said they used eucalyptus for coughs, colds, sore throats, or sinusitis (EMA). Eucalyptus oil also became a standard partner of camphor and menthol in vapor rubs and lozenges, the products most people now associate with its smell.

Modern regulation draws a sharp line between long use and proof. EMA’s herbal committee adopted its monograph on eucalyptus leaf in 2013 and on eucalyptus oil in 2014, recognizing both as traditional herbal medicines: effectiveness is considered plausible because the products have been used safely for at least 30 years, including 15 in the EU, not because trials have demonstrated it. The committee examined the cineole trials in bronchitis and asthma but concluded that firm conclusions could not be drawn because they did not use eucalyptus oil itself. A revision of the oil monograph, adopted in November 2024 and published in February 2025, added allergic reactions, stomach upsets, and contact eczema as side effects and, to be consistent with other essential-oil monographs, changed the age limits: oil medicines are now contraindicated under 24 months rather than 30, and rubs, inhalations, and baths are accepted from age 3 rather than 4. A 2022 review of the leaf monograph found no reason to change it, so leaf preparations remain contraindicated under 30 months. In the United States, eucalyptus oil is not itself on FDA’s list of topical cough-suppressant ingredients, which names only camphor and menthol, but the rules permit it at 1.2–1.3% alongside them in an ointment, as in Vicks VapoRub (camphor 4.8%, menthol 2.6%, eucalyptus oil 1.2%).

Much of eucalyptus’s appeal is a trick of the senses, though a useful one. Burrow, Eccles, and Jones (Acta Oto-Laryngologica 1983) had volunteers breathe camphor, eucalyptus, or menthol vapor for five minutes and measured the resistance to airflow through their noses. None of the vapors changed nasal resistance, yet most people reported a cold sensation in the nose and a feeling that air was flowing more freely; exercise, by contrast, genuinely lowered resistance without producing that sensation. The authors concluded that these aromatics stimulate cold receptors in the nose. EMA accepts this as support for the plausibility of eucalyptus inhalation for comfort in a congested nose, but it is a sensation of better airflow, not a measurably wider airway. A similar caution applies to rubs. In a 1980 experiment cited by EMA, a single 7.5 g dose of eucalyptus oil in a petrolatum base massaged onto the chest reduced coughing provoked by inhaled citric acid in 32 healthy volunteers for up to an hour and a half, but EMA judged artificial cough experiments of this kind to have no clinical relevance.

Cineole itself is readily absorbed. EMA summarizes studies showing that inhaled cineole reaches its peak level in the blood after about 18 minutes and, after a 10-minute inhalation, has a plasma half-life of about 36 minutes, while cineole taken by mouth is almost completely absorbed. Once in the body it has measurable effects on airway defenses. In a study by Juergens and colleagues cited by EMA, 200 mg of cineole three times a day for three days suppressed production of two inflammatory messengers, leukotriene B4 and prostaglandin E2, by stimulated blood monocytes from people with asthma and from healthy volunteers, and in cell culture cineole inhibited cytokines such as TNF-α, IL-1β, IL-4, IL-5, and IL-8 at concentrations achievable in the body. Cineole also seems to speed the clearing of mucus: 200 mg four times a day for four days improved mucociliary clearance in 12 people with chronic obstructive lung disease, and four days of 200 mg three times a day raised the beating rate of cilia brushed from the nose by 8.2%, compared with 1.7% on placebo. EMA concluded that these human data support the plausibility of the traditional use in cough.

Laboratory studies add antimicrobial activity. In cell culture, pharmacopoeia-grade eucalyptus oil at 0.01% reduced herpes simplex virus levels by 58–75%, vaporized oil reduced influenza A infection by 78%, and in other experiments the oil inhibited a range of bacteria at concentrations of 0.25–2%, though one study found no effect on any strain tested (EMA). None of this shows that breathing eucalyptus vapor or taking capsules clears an infection in people. Dose matters too, which is why tea, rubs, and capsules are not interchangeable. EMA calculated that even if all the oil in the leaf passed into the water, a single cup of eucalyptus tea would contain roughly 11–100 mg of cineole and a full day’s tea at most about 300 mg, and in practice much less reaches the cup: for sage tea, only 23–36% of the cineole transfers. A traditional eucalyptus tincture provides about 1–19 mg of cineole a day, which EMA says is not supported by the clinical data. The main capsule trials, by comparison, gave 600 mg of cineole a day by mouth.

Cough with a cold is eucalyptus’s officially recognized use. EMA’s monograph on eucalyptus leaf covers relief of cough associated with a cold, using dried leaf as a tea or a steam inhalation for adolescents and adults, or a tincture for adults only. Its monograph on eucalyptus oil, revised in 2024, covers the same indication and adds symptomatic relief of localized muscle pain. For cough, the oil can be taken by mouth in measured doses by adolescents and adults, inhaled from hot water, rubbed onto the chest and back, or added to a bath; for muscle pain it is rubbed onto the aching area or used in a bath, after a doctor has ruled out serious causes. All of these are traditional uses, accepted because the products have been used safely for decades and their effect is plausible, not because trials of eucalyptus leaf or oil have shown benefit. EMA asks people to see a doctor if breathlessness, fever, or pus-like phlegm develops, if symptoms worsen, or if a cough lasts more than a week, and to seek advice if muscle pain lasts more than two weeks with rubs or one week with baths, or if the painful area becomes red or swollen.

The best clinical evidence concerns purified cineole capsules, which are sold as licensed medicines in parts of Europe and which EMA treats as supportive evidence because cineole makes up at least 70% of the oil. Kehrl and colleagues (Laryngoscope 2004) randomized 152 adults with acute non-purulent rhinosinusitis, sinus inflammation without pus, to two 100 mg cineole capsules three times a day or placebo for seven days. Symptom scores started at 15.6 in both groups; after seven days they had fallen to 3.0 with cineole and 9.2 with placebo, with improvements in headache, nasal blockage, and discharge. Two people on cineole had mild side effects, heartburn and a rash. In a comparison trial of 150 adults cited by EMA, cineole beat a five-herb combination product on sinus headache, nasal blockage, and discharge over a week. Fischer and Dethlefsen (Cough 2013) gave 242 adults with acute bronchitis 200 mg of cineole or placebo three times a day for ten days; after four days the cineole group had improved significantly more on a bronchitis symptom score, especially in the frequency of coughing fits. Uncontrolled observational studies cited by EMA, including one in 336 children aged 2 to 11, reported good tolerance, but without a comparison group they cannot show benefit. Eucalyptus oil is also about two-thirds of Myrtol (ELOM-080, sold as GeloMyrtol forte), an enteric-coated distillate of eucalyptus, sweet orange, myrtle, and lemon oils in a 66:32:1:1 ratio. In placebo-controlled trials it cut coughing fits more than placebo in 413 adults with acute bronchitis (Gillissen and colleagues, Drug Research 2013) and eased acute viral sinusitis sooner in 463 people (Pfaar and colleagues, Laryngoscope 2023), but those results belong to the four-oil product rather than to eucalyptus alone.

Two six-month trials tested cineole as an add-on to usual treatment for chronic lung disease. Worth, Schacher, and Dethlefsen (Respiratory Research 2009) randomized 242 people aged 40 to 80 with stable, moderate to severe COPD to 200 mg of cineole or placebo three times a day through the winter; the frequency, duration, and severity of flare-ups were lower with cineole, and lung function, breathlessness, and quality of life improved more than with placebo, with similar adverse events in both groups. Worth and Dethlefsen (Journal of Asthma 2012) gave the same dose to 247 people with asthma for six months and reported significant improvements in lung function (FEV1), asthma symptoms, and asthma-related quality of life. These are encouraging results, but they come largely from one research network: Uwe Dethlefsen is a co-author of the sinusitis, bronchitis, COPD, and asthma trials, and the bronchitis and COPD trials were funded by Cassella-med. EMA treats them only as support for traditional use. In these trials cineole was added to prescribed treatment, not substituted for it, and it is never a replacement for inhalers or other prescribed medicines.

Vapor rubs, in which eucalyptus oil is a minor partner to camphor and menthol, have one notable trial. Paul and colleagues (Pediatrics 2010) randomized 138 children aged 2 to 11 with colds to a single bedtime application of Vicks VapoRub, petroleum jelly, or nothing on the chest and neck. Parents rated the vapor rub best for night-time cough, congestion, and sleep, both the child’s and their own; petroleum jelly was no better than nothing. Irritant side effects, such as a burning sensation of the skin, nose, or eyes, were more common with the vapor rub. Blinding was only partial, because the rub has a strong smell and the no-treatment group knew it was untreated; the outcomes were parent reports after a single night; and the study was supported in part by an unrestricted grant from Procter & Gamble, which made Vicks at the time. It shows short-term comfort rather than faster recovery. Steam inhalation with eucalyptus has not been tested in good trials, and EMA’s case for it rests on the cooling sensation described above. The traditional dose is modest: 3–8 drops of oil in 250 ml of boiling water, up to three times a day for adults, with the eyes kept out of the steam.

Beyond cough and colds, the claims outrun the evidence. Folk medicine has used eucalyptus internally for asthma, fever, flu, whooping cough, poor appetite, bladder and kidney infections, diabetes, and rheumatism, and externally for wounds, acne, ulcers, and bleeding gums; EMA notes that none of these uses has been confirmed scientifically. Eucalyptus oil turns up in dental products, hair products, and cleaners, and Poison Control lists a long catalog of popular uses, from sinus congestion and seasonal allergies to headache, dandruff, and head lice, but a long list of uses is not evidence for each one. Neither EMA nor any trial described here supports using eucalyptus to prevent colds, boost immunity, or treat influenza, COVID-19, pneumonia, or whooping cough, and a child who is struggling to breathe needs medical care, not more vapor. Insect repellent is a separate story. CDC lists oil of lemon eucalyptus among the EPA-registered repellent ingredients it recommends, but that product comes from a different tree and relies on a different chemical, PMD, and CDC says the effectiveness of unregistered natural repellents is unknown, so ordinary eucalyptus oil should not be relied on to prevent mosquito bites.

Eucalyptus leaf is sold cut and dried for tea and steam inhalation, and as tinctures. EMA’s dose for adolescents and adults is 1.5–3 g of cut leaf infused in 150 ml of boiling water, up to four times a day (4.5–12 g daily), or 3 g of leaf in boiling water as an inhalation, up to three times a day. A 1:5 tincture made with 68–80% alcohol is limited to adults, at 2.5 g up to four times a day, partly because of its alcohol content. Leaf preparations must not be used in children under 30 months, are not recommended under 12 for the tea or under 18 for the tincture, and should prompt a visit to a doctor if symptoms last more than a week. The tea tastes pungent and camphor-like. Its cineole content is modest and variable, as EMA’s calculations show, so a cup of eucalyptus tea is a gentle traditional remedy rather than a substitute for the doses tested in capsule trials. Do not make a “stronger tea” by adding drops of essential oil to a mug: that turns a leaf remedy into swallowed oil, which is how many poisonings begin.

Eucalyptus oil medicines in the EU come in several forms, each with its own dose. For adolescents and adults, oral forms supply 100–200 mg of oil two to five times a day, up to 600 mg daily; EMA notes that licensed capsules are made gastro-resistant and that oil drops should be taken with a glass of water. For inhalation, adults use 3–8 drops in 250 ml of boiling water three times a day, and children aged 3 to 11 up to 2–4 drops. For rubs, a few drops of oil, or a thin layer of an ointment containing 10% eucalyptus oil, are applied to the chest and back two or three times a day, from age 3. Bath additives provide 1.5–6 g of oil per 100 liters of water for adults with a cold (0.5–3 g for children aged 3 to 11), at 35–38°C for 10–20 minutes, three or four times a week. Full hot baths are contraindicated with large wounds, acute skin disease, high fever, severe infection, serious circulatory problems, or heart failure. In the United States, over-the-counter vapor-rub ointments may contain 1.2–1.3% eucalyptus oil, always combined with camphor and menthol.

Practical points: check the label to see whether you have dried leaf, a finished oil medicine, a combination rub, or a bottle of essential oil sold for aromatherapy, because only finished medicines come with tested doses and age limits. Never use undiluted oil on the skin, never put oil or rubs in or under the nose, and keep oil away from the eyes; wash your hands after applying it, since EMA warns that touching the eyes with unwashed hands can irritate them. Do not apply oil to broken or irritated skin. For steam, use a bowl on a stable surface, close your eyes, keep your face at a comfortable distance, and never leave a child alone with hot water; EMA stresses caution to avoid burns. Diffusers and vaporizers spread oil into the air and leave a reservoir of liquid that a child can reach, and Poison Control advises keeping children away from vaporizer liquid and buying products with child-resistant closures. Store every eucalyptus product, including lozenges, rubs, and bottles of oil, up high and out of sight, and treat any swallowed oil as an emergency.