A trunk with white bark peeling in thin, papery layers. Narrow, thick leaves that smell cool when crushed. In Lộc Thủy, Hue, the leaves of this tree are cut from March to August, taken to the still, and give an oil with 40 to 60 percent 1,8 cineole.
Cajuput forest on low wet ground
Cajuput is a tree of difficult ground. Melaleuca cajuputi grows wild on sandy and waterlogged soils, from the central coastal strip down to the U Minh forests in the far south. In U Minh Hạ National Park it covers almost 89 percent of the area. Few trees handle such ground as well.
The name cajuput comes from the Malay and Indonesian kayu putih, meaning white wood or white tree. The name points straight at the bark: grey, pale brown or white, peeling in thin, papery layers. In Vietnamese the tree is called tràm gió; in English it also goes by names such as swamp tea tree or river tea tree.
It belongs to the myrtle family (Myrtaceae), the same family as eucalyptus, and to the same genus Melaleuca as tea tree and niaouli. The library records commercial cajuput oil as produced in Vietnam, China and Indonesia. The oil was once thought to come from another species, Melaleuca leucadendra; that name survives in some older sources.
On low, wet ground, cajuput forest was there before any still. The trees grow densely, with straight trunks and narrow crowns. For growers, cajuput is timber, a tree that holds the soil, and a source of leaves. Essential oil is only one of the things it gives.
The library page on essential oils of Vietnam places cajuput right after cassia and star anise among the aromatic crops grown at scale in the country. For cajuput, the centre is not the largest forest area but the place where distilling is concentrated.
Cajuput leaves into the still
Cajuput distilling is concentrated in Lộc Thủy, Phú Lộc, in Hue. Leaves and young twigs are cut, packed into the still and steam distilled. The library records the distilled material as leaves and twigs; the trunk is left standing to grow new leaves.
Leaves are cut mainly from March to August, in the dry season. This is when the cineole content of the leaf runs higher. The harvest calendar in the library lists all six months, March to August, for cajuput, matching this window.
In 2020, Hue cajuput oil received a geographical indication, number 00096. The file specifies 1,8 cineole from 40 to 60 percent. The Vietnamese Pharmacopoeia sets a slightly narrower requirement, 45 to 60 percent. These two figures are the frame a bottle of Hue cajuput oil needs to sit within.
Cineole content is the easiest way to read the quality of a batch of cajuput oil, but also the easiest point to fake. The library notes that cajuput oil may be extended or replaced with eucalyptus oil, which is also rich in cineole. Oils from M. quinquenervia or M. symphyocarpa are also used to cut it. Occasionally fixed oils or kerosene are added.
A bottle of cajuput oil with a geographical indication therefore says more than where it grew. It binds a range of cineole, and indirectly, the season of the cut.
Cineole: the cool scent of the leaf
The cool scent of cajuput leaves comes from a molecule whose name is tied to the tree itself. 1,8 cineole is also called eucalyptol, and also cajeputol. Its formula is C₁₀H₁₈O, molecular weight 154.25 g/mol. Structurally it is a bicyclic ether of the monoterpenoid group.
The library describes the scent of cineole as camphor, eucalyptus, cool and sharp. It is the molecule that defines rosemary and eucalyptus. Cineole occurs in over 200 essential oils, from Eucalyptus globulus with 65.4 to 83.9 percent, to rosemary, cardamom and cajuput.
In cajuput oil, cineole makes up 41.1 to 70.8 percent according to the library's combined data. The remainder is not small. Alpha terpineol from 6.5 to 8.7 percent. Linalool from 2.7 to 3.6 percent. Limonene, gamma terpinene, p cymene, terpinolene and alpha pinene at a few percent each. A little beta caryophyllene and guaiol.
That remainder is what separates cajuput from eucalyptus. Both oils carry the cool scent of cineole, but cajuput adds alcohols and sesquiterpenes that make it rounder and warmer. Alpha terpineol has a light floral line; linalool is soft; guaiol and caryophyllene add a little wood underneath.
On a blotter, cajuput opens with cineole: cool, direct, slightly pungent. Then, as some of the cineole evaporates, the lower layer appears, slightly sweet and slightly woody. In Eucalyptus globulus that lower layer is much thinner.
Three Melaleuca relatives
Three trees of the genus Melaleuca give three oils that buyers often confuse. Cajuput, M. cajuputi. Tea tree, M. alternifolia. Niaouli, M. quinquenervia. All three belong to the myrtle family, all are distilled from leaves, and all carry English names that include tea tree.
Tea tree is a small shrub endemic to the North Coast of New South Wales, Australia, growing wild in wetlands and along streams. The library records that the name tea tree is attributed to Captain James Cook in 1770. Commercial distillation began in the 1920s. The plant needs 18 to 24 months from planting to its first cut, after which it can be cut once or twice a year for 15 to 20 years.
Niaouli is a medium sized tree native to Australia and New Caledonia, also growing wild in Madagascar. The most common commercial oil is the cineole chemotype, produced mainly in Madagascar, with 40 to 65 percent 1,8 cineole, alpha pinene from 8 to 15 percent, limonene from 5 to 10 percent and viridiflorol up to 8 percent.
Chemically, cajuput and niaouli are close: both are cineole oils. Tea tree stands apart. Its main molecule is terpinen 4 ol, from 30 to 45 percent, with gamma terpinene and alpha terpinene. The ISO 4730 standard requires tea tree oil to hold at least 30 percent terpinen 4 ol and no more than 15 percent cineole. Put another way, high cineole is a good sign in cajuput and a poor sign in tea tree.
That reversal explains why mixing between the three oils can be detected. The library notes that cheap tea tree oil is sometimes cut with cajuput, niaouli or eucalyptus oils, and chiral GC MS analysis is the check.
Cajuput and tea tree on a blotter
Two blotters side by side show how far two related trees can drift apart. The cajuput blotter opens cool, close to eucalyptus, then moves into a rounder, slightly sweet layer. The tea tree blotter opens sharp, with a medicinal edge, lightly camphoraceous, and a touch of spice.
The library describes tea tree oil as sharp, medicinal, lightly camphoraceous, fresh and slightly spicy. Terpinen 4 ol, its main molecule, is described as fresh, lightly woody, clean, suggestive of cardamom, with an earthy finish. That earthy finish is what cajuput lacks.
Freshly distilled tea tree oil has a clear medicinal note. The library notes that 6 to 12 months of storage softens the scent, but also raises the peroxide value, meaning the oil has begun to oxidise. It is an unusual trade: a gentler scent comes with a less stable bottle.
Same genus, same English name, two different scents. The Vietnamese names, tràm gió and tràm trà, keep that difference better than the English ones.
Cineole and safety notes
Cineole is a molecule of low allergenic concern on adult skin, but it has a clear limit with young children. The library records that across six large studies in patients sensitive to tea tree oil, 1,8 cineole did not cause sensitisation; the compound is classed as not significantly allergenic.
The main caution concerns the airways of young children. Oils rich in 1,8 cineole can cause central nervous system and breathing problems in young children when applied near the nose; the library notes a risk of laryngospasm. For cineole itself the recommendation is to avoid the face, nose and mouth of children under 30 months. For cajuput oil, the library records a contraindication: do not apply to or near the face of infants and young children.
For niaouli, also rich in cineole, the library records a recommendation to keep it away from the face of children under 6. It is the same caution, from the same molecule, recorded with different age thresholds depending on the reference.
In adults, the library records cajuput oil as a low risk for skin sensitisation and irritation, and not phototoxic. For pregnancy, the library notes cajuput oil is likely not hazardous based on data for its main constituents; general notes on essential oils in pregnancy are gathered in a separate piece. This piece says nothing about effects of cajuput on the body.
A cool molecule, a white bark peeling like paper, a cineole range written into a geographical indication file. What remains belongs to dose and distance.
White wood, cool leaves, a molecule named after the tree.
High cineole is a good sign in cajuput and a poor one in tea tree.
One genus, two ways to read the same number.