The eucalypts (Eucalyptus spp.) occupy a genus of about 500 trees in all habitats of Australia. Some eucalypts such as bloodwood (Eucalyptus gummifera) secrete an edible gum, others have a starchy root bark, while the flowers of many species produce a sweet nectar. Some gum-tree exudates such as manna can be collected and then soaked together with honey or nectar to make an edible liquid that sets much like jelly. The seeds of a few species may also be eaten, including the river red gum (Eucalyptus camaldulensis) and blue mallee (Eucalyptus gumophylla), while the roots of other gum-trees can be dug up and tapped in order to obtain drinking water.¹

The leaves of the gum-tree are inedible to humans as well as most animals because of the natural insecticides and compounds the tree secretes to suppress competing plants that try to grow under its canopy. The koala is an exemption, having developed a specially adapted digestive system which relies on a relatively large cecum. The Aboriginals use various parts of the gum-trees as a medicine, a practice adopted by the white colonial settlers long ago, but with less diverse applications. For example, the bark or inner wood of eucalypts contains strong tannins that can be used for treating dysentery; poultices can be made from the bruised and heated leaves to treat aches and rheumatism; saps and resins can be collected and concentrated to make a disinfectant for treating sores, cramps, cuts, ulcers, and burns; while nectar is used for treating coughs and colds, also an infusion of the leaves. Furthermore, headache can be treated by inhaling the steam from the leaves much as we would do in the city by putting a few drops of eucalyptus oil in a bowl of boiling water then leaning over it with a tea towel draped on our heads.¹

Scientific research has confirmed the traditional usage by identifying a number of active constituents present in Eucalyptus oil, especially from the gumtree Eucalyptus globulus. These constituents include 1,8-cineole, α-pinene, terpinene and p-cymene which are all also found to a lesser extent in tea tree oil. The percentage varies with the species and location. The new species Eucalyptus polybractea has been planted in large numbers in recent years; a gum which grows from a deep root and has multiple trunks that can be coppiced repeatedly, because of its particularly high cineole content.

Eucalyptus oil is anti-inflammatory and antioxidant in activity, and is particularly useful in treating respiratory diseases where it reduces a tendency to hypersecretion in conditions such as sinusitis, bronchitis, and asthma. The spasmolytic activity of the oil also contributes to airway treatment by relaxing the muscles of the airway walls. In addition, it has antimicrobial activity against a range of organisms that cause respiratory infections including Haemophylus influenza and Mycobacterium tuberculosis (TB), but broadly speaking it is an immune stimulant, capable of enhancing the activity of white blood cells, especially phagocytes.

Eucalyptus oil can also be applied topically to infected wounds and rashes. In laboratory tests it has demonstrated antimicrobial activity against Staphylococcus aureus, antiviral activity against Herpes simplex, and because it has antifungal activity as well, it can be used to treat infections such as tinea and Candida albicans.²

The Aboriginals understood the diverse medicinal properties of Australian trees and plants and established them in an enduring clinical practice, having determined them empirically over 50,000 years or so. This herbal lore is thought to have been largely lost since colonial settlement, as with traditional lore in places like the Amazon, where development and urban expansion have shown a profligate disregard for nature’s disappearing bounty. Ironically, it is only with cutting-edge technology that the long-standing traditional usage is often verified, gaining in the process the accreditation of a modern evidence-base.

We should, however, be careful where we store this seemingly-innocuous oil because even natural plants and their extracts can be as potent and dangerous as modern drugs. In this case, if pure eucalyptus oil is ingested in amounts as little as 5 ml it will cause epileptic fits in children, and in amounts up to 30 ml, can be fatal.³

Disclaimer: this article is intended for the purpose of general education only, and is not a substitute for diagnosis, treatment advice, or a prescription that is given in a consultation with a qualified physician.

References:

1.         Isaacs J. Bush Food, Aboriginal Food And Herbal Medicine. Weldon; 1987.

2.         Sadlon AE, Lamson DW. Immune-modifying and antimicrobial effects of Eucalyptus oil and simple inhalation devices. Altern Med Rev J Clin Ther 2010;15:33–47.

3.         Kumar KJ, Sonnathi S, Anitha C, Santhoshkumar M. Eucalyptus Oil Poisoning. Toxicol Int 2015;22:170–1.