• Gwenda Kyd

Guest Blog - Eucalyptus

Eucalyptus – one of Australia’s gifts to the world…and aromatherapy

In aromatherapy, the essential oil obtained from Eucalyptus globulus is a treatment for respiratory issues. In addition, it is used as an antiseptic, antispasmodic, decongestant, diuretic and stimulant. It has cooling properties, which gives it deodorising characteristics and it helps fight migraines and fevers. This cooling capability also helps with muscle aches and pains. However, it should be avoided by people with epilepsy. In this blog, we’ll take a closer look at the tree and find out about some of its other uses.

E. deglupta (rainbow eucalyptus) bark
E. deglupta (rainbow eucalyptus) bark; ©Adobe Stock

Eucalyptus is a genus of over 700 hundred trees, the majority of which are found in Australia. Their name means well-covered, referring to the woody bud cap (or operculum) with which the developing flowers are protected. The trees produce a new layer of bark every year and the old outer bark dies. In about half of the species, the dead bark is shed. After shedding its dead bark, the new bark of rainbow eucalyptus (E. deglupta, found at the northernmost edge of the genu s’ range, in New Guinea) is green, but becomes multi-coloured as it matures.

Koala; Syahir Hakim from Pixabay
Koala; Syahir Hakim from Pixabay

Koalas can eat about 200–500g of eucalyptus leaves a day. The leaves are not very nutritious and contain fibres which make them hard to digest, so extracting the nutrients uses a lot of energy. Koalas save energy by sleeping for up to 22 hours a day! Toxic oils protect the trees from most animals, but koalas are immune. They identify eucalyptus trees by the characteristic medicinal smell. This may also have attracted humans to try the leaves for their medicinal benefits.

Once believed to be a cure for malaria, French Trappist monks replaced swamps and scrub with the trees. However, although they do have some antiseptic properties, it was probably the removal of the swamps – breeding grounds for malaria-carrying mosquitos – by the thirsty trees, that had the observed beneficial effect.

Their high water consumption means deep roots are necessary and this can be useful for identifying minerals buried far underground. Trees in the Australian outback have been found to draw up tiny particles of gold from tens of metres below, through their roots. These particles, and those of other metals, are visible using X-ray elemental imaging but would be untraceable using other methods. The microscopic nuggets identified in the leaves are not worth collecting in themselves – it would take the gold found in 500 large trees to produce one wedding ring – but the trees do provide an environmentally friendly way of locating gold and other metal deposits.

Eucalyptus sp. in Kew Gardens
Eucalyptus sp. in Kew Gardens

Eucalyptus trees release volatile compounds like pinenes (as do pine trees and rosemary bushes). In the presence of sunlight, pinenes react with ozone and other particles in air to produce nanoparticles. Due to their size, these split white light from the sun into its component colours. As blue light is scattered most, the trees can appear to be shrouded in a blue haze. This cools down the trees, giving them some degree of temperature control. It’s also the reason why the Blue Mountains in New South Wales are blue.

Eucalyptus leaves also contain up to 70%, and the essential oil up to 90%, eucalyptol (1,8-cineole). This has proven effects against asthma and airway mucous hypersecretion, anti-inflammatory activity and some anti-cancer activity. It is often an ingredient in mouthwashes and cough suppressants and is used in a wide range of fragrances and flavourings. And even the hollowed-out trunks of eucalyptus can find a use…they can be made into didgeridoos.

Gwenda Kyd is a chemist, writer and Bach flower remedy practitioner.

She is running a course on Aromatherapy Plants: The smell of good health at the Cambridge University Botanic Garden on 23rd April 2022. For more details and to book go to their website.

Gwenda's book, The Plants of Dr Bach, is available from Emma Kenny Massage Therapies and online at https://www.cambridge-bach.co.uk/plants-dr-bach/.

You can also find more plant blogs by Gwenda at https://www.cambridge-bach.co.uk/blog/.



Bill Laws (2010); Fifty Plants that Changed the Course of History; Quid Publishing, ISBN 978-0-7153-3854-4


Rebecca Morelle (2013); https://www.bbc.co.uk/news/science-environment-24628241

Joseph Nordqvist (2018); The health benefits of eucalyptus; https://www.medicalnewstoday.com/articles/266580.php