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The melaleuca is a tall-growing tree, native to eastern Australia, Myanmar (Burma), New Guinea, the Solomon Islands, and the East Indies. It is also planted elsewhere in the tropics and is rather common in greenhouses. The species Melaleuca alternifolia, one type of tea tree, is unique to Australia and native to New South Wales.

The melaleuca tree grows 20 to 33 m in height and has a slender crown. The tree is usually single-trunked, but may develop multiple trunks. The most striking feature is its almost pure-white papery bark, peeling off in sheets. The leaves are greyish-green, 4 to 10 cm long, 2 cm wide, and stiff. The leaves are very aromatic.

Melaleuca’s beautiful flowers bloom whitish-pink or purple. They have prominent ivory-white stamens and are produced on bottlebrush-like spikes 16 cm long. Dust-like seeds are enclosed in rounded, tightly clustered, greyish-brown woody capsules produced along the stems. In Australia, melaleuca flowers from October to December; in California and Florida in the USA, from June to November.

The trees grow along creek banks. Some species have weeping foliage; others are stiffer in appearance.

Melaleuca oil (cajeput oil) is distilled from the fresh leaves and twigs. The oil is obtained from several species besides Melaleuca leucadendron. Similar oil, tea tree oil, is usually extracted from a family member, Melaleuca alternifolia. Melaleuca oil is used in medicine and for a variety of other purposes. The principal constituent of the oil is cineol. Solid terpineol is also present, and several aldehydes, such as valeric, butyric and benzoic.

The spongy bark was used by the Aborigines of Australia to make shields and canoes, for roofing, and as timber.

IgE-mediated reactions

Melaleuca pollen can induce asthma, allergic rhinitis and allergic conjunctitivis. (1-3)

In a study in Darwin, Australia, that correlated daily average ambient pollen and fungal spore concentrations with hospital admissions for allergic respiratory disease, the association was the strongest in the case of Myrtaceae pollen (this being the dominant tree taxa in the region). (3,4)

In an early study, pollen extracts of the trees Callistemon citrinis (bottlebrush) and melaleuca, as well as of Bahia grass, were analysed for antigenic and allergenic cross-reactivity. Clinical studies demonstrated that 81% of the patients who were skin-test-positive to at least 1 of the pollens were also positive to the other 2. (1)

In a study of the closely-related paperbark tea tree (M. quinquenervia), a 2-year aeroallergen survey and skin-test results from 1 017 subjects were reviewed. Ninety-seven of 1 017 subjects were at 2+ or greater in intradermal tests. One of 6 double-blind nasal challenges and 1 of 4 single-blind bronchial challenges using extract from this tree were positive in subjects with positive skin tests. The study concluded that the paperbark tea tree is not a significant source of aeroallergens. (5)

In a Malaysian study of 200 patients attending a clinic, of the 29.5% who were asthmatic with positive SPT reactions, 21.5% had reactions to 1 or more of the grass pollens, 21.5% to Acacia pollen and 7.5% to melaleuca pollen. (6)

Other reactions

Tea tree oil (melaleuca oil) is an essential oil, distilled predominantly from the leaves of the Australian plant Melaleuca alternifolia. This species is unique to Australia and native to New South Wales. Allergic contact dermatitis to tea tree oil is well recognised and is becoming increasingly common in Australia. (7-9)

Multiple antigenic components between 29 and 66 kDa have been detected, but the allergens have not yet been categorised. (1)

Cross Reactivity

Extensive cross-reactivity between the different individual species of the genus could be expected. (10)

Clinical studies demonstrated that 81% of the patients who were skin-test-positive to pollen from Callistemon citrinis (bottlebrush), M. leucadendron, or Bahia grass (Paspalum notatum) were also positive to the other 2. (1)

RAST inhibition analysis has demonstrated cross-reactivity between the closely-related Melaleuca quinquenervia and bottlebrush (Callistemon citrinis). (6)

Last reviewed: May 2022