A dried piece of cassia bark, rolled into a tube, reddish brown. Two mountain regions of Vietnam produce bark like this, and two geographical indication files record two different oil figures: Văn Yên from 4.38 to 6.07 percent, Trà My from 8.93 to 10.91 percent.
Two cassia regions, one tree
The cassia grown in Vietnam is mainly Cinnamomum cassia, a tree of the laurel family (Lauraceae), native to China and Southeast Asia. The currently accepted name is C. aromaticum, but cassia remains the common name in the essential oil trade. In the Lê Mai library the species has its own page: cassia.
The largest cassia area lies in Lào Cai after the July 2025 provincial mergers, a province that now includes Văn Yên district of former Yên Bái. It holds about 143,000 hectares of cassia, nearly three quarters of the national area. Each year the region harvests 40,000 to 45,000 tonnes of dried bark and over 200,000 tonnes of twigs and leaves. Văn Yên cassia is a name tied to volume.
Trà My cassia lies further south, in the mountains of former Quang Nam, now part of Đà Nẵng. Locally the variety is called “cao sơn ngọc quế”. The area is far smaller, but the trunk bark carries more oil. Trà My cassia is a name tied to concentration.
This section heading speaks of one tree, and that holds for Văn Yên. For Trà My the answer is still open. Some sources place Trà My cassia in Cinnamomum loureiroi, the species sold internationally as Saigon cinnamon; the geographical indication file names only the genus Cinnamomum. This piece keeps that uncertainty rather than choosing an answer.
At national scale the numbers grow much larger. In 2023 Vietnamese cassia led the world by export value. In 2025 the country shipped 120,295 tonnes of cassia, worth 300.2 million USD. Most of it is dried bark. Essential oil is a small part of that flow, and it usually comes from what remains once the bark has been peeled.
Bark, leaf and young twigs: three parts of the tree
A cassia tree is harvested in order. The bark comes off first, because bark is the main commodity. Small branches and leaves remain, and this is the material that goes into the still. The library page on essential oils of Vietnam states it plainly: cassia oil is mainly distilled from twigs and leaves, what is left after peeling.
What stands out is how close cassia leaf and bark oils are. A leaf oil sample from Yên Bái gave about 90 percent trans cinnamaldehyde; bark oil about 93 percent. The wider data in the library give a broader span: cassia bark oil from 73.2 to 89.4 percent (E) cinnamaldehyde, leaf oil from 54.6 to 90.1 percent. Two parts of the tree speak the same language.
Oil content in the bark is where the two regions part. The Văn Yên geographical indication records 4.38 to 6.07 percent oil in the bark, with 84.9 to 90.1 percent cinnamaldehyde in the oil. Trà My trunk bark holds 8.93 to 10.91 percent oil, close to twice as much. For the same weight of bark, Trà My holds more oil.
In Ceylon cinnamon the story is entirely different. The bark oil and leaf oil of Cinnamomum verum are almost opposite liquids. The bark oil is rich in cinnamaldehyde. The leaf oil holds 68.6 to 87 percent eugenol, and cinnamaldehyde drops to about 0.6 to 1.1 percent. One tree, two scents: one is cinnamon, the other close to clove.
So the name on a bottle needs the plant part as well. “Cinnamon oil” is not enough to know what is inside. Species, the part distilled and the growing region together give an answer.
Cinnamaldehyde and the heat of cassia
One small molecule decides almost the whole scent of cassia. Cinnamaldehyde has the formula C₉H₈O and a molecular weight of 132.16 g/mol, and belongs to the phenylpropenoid aldehydes. The library describes its scent as warm and spicy, sweet, with cassia character. When this molecule makes up nine tenths of the bottle, the rest is only enough to adjust the shading.
Cinnamaldehyde exists in two geometric forms, (E) and (Z). The (E) form dominates. The (Z) form in cassia oil ranges from 0.4 to 12.3 percent. Alongside come cinnamyl acetate, up to about 12.5 percent, which adds a softer line; benzaldehyde from 0.4 to 6.3 percent, the molecule behind bitter almond; salicylaldehyde; and a small amount of coumarin.
The heat of cassia on a blotter comes from that ratio. One molecule dominates, few others soften it. The scent opens dry, sharp and sweet in the manner of burnt sugar, then holds that direction for a long time. There are not many shifting layers, as there are in oils with dozens of constituents in balance.
Because cinnamaldehyde is easy to synthesise, cassia oil is also easy to adulterate. The library lists the usual additions: synthetic cinnamaldehyde, methyl cinnamic aldehyde and coumarin. A bottle with a fine cinnamaldehyde figure on paper has not necessarily come from cassia twigs and leaves. Chromatography gives the composition, but provenance still needs documents to go with it.
Coumarin is a small detail with weight. Coumarin smells of freshly cut hay, sweet like honey. In cassia oil it is present from trace levels up to about 2.5 percent. Cassia is one of the few essential oils with natural coumarin, and this is one marker that separates cassia from Ceylon cinnamon.
Cassia and Ceylon: two names for two species
The two barks differ first in thickness. Cassia bark is thicker, with a heavier, hotter scent. Ceylon cinnamon, Cinnamomum verum, also called C. zeylanicum, is a tree of Sri Lanka and southern India. In many languages both are called cinnamon, and the confusion starts there.
Ceylon cinnamon bark oil is steam distilled from the dried inner bark of young trees. Cinnamaldehyde is still the main constituent, from 63.1 to 75.7 percent, lower than in cassia. The rest is richer: eugenol from 2 to 13.3 percent, linalool up to 7 percent, beta caryophyllene from 1.3 to 5.8 percent, a little p cymene and 1,8 cineole.
Those minor constituents change the scent. Eugenol brings a clove edge. Linalool brings a floral edge. On a blotter, Ceylon cinnamon is softer and rounder, with a floral line and a spice line beneath the cinnamon. Cassia goes more directly: hot, dry, with few layers.
Sri Lanka produces two qualities of bark oil. The premium grade is distilled from the inner bark. The second is distilled from chippings and shoot bark, with lower cinnamaldehyde and eugenol that can reach 20 percent. The library also notes a commercial reality: cassia oil or reconstituted oils are sometimes sold under the name of Ceylon cinnamon bark.
Coumarin is the clearest point of difference. Cassia contains coumarin; true Ceylon cinnamon does not. In note lists published by perfume houses, Ceylon cinnamon bark appears in bottles such as Yves Saint Laurent Opium from 1977 and Dior Dioressence from 1969, both in the heart. The cinnamon named on a perfume box and the cinnamon in a still do not always point to the same tree.
Peeling seasons and geographical indications
Cassia bark is peeled in two rounds a year, by the lunar calendar: months 2 to 3, and months 8 to 9. Autumn bark carries more oil than spring bark. The timing of the peel is not only a matter of work schedules; it changes the oil figure in every piece of bark.
Geographical indications are granted by Vietnam's Intellectual Property Office, confirming that a product's qualities are tied to the land where it is made. For aromatic crops the file usually records oil content and key constituents. It is one of the rare places where a scent is written as a specification that can be checked.
Cassia holds four geographical indications in Vietnam. Văn Yên cassia, number 00018, granted in 2010, specifies 4.38 to 6.07 percent oil in the bark and 84.9 to 90.1 percent cinnamaldehyde. Trà My cassia, number 00029, granted in 2011, specifies 8.93 to 10.91 percent oil in the trunk bark. Thường Xuân cassia, number 00051, in 2016. Trà Bồng cassia, number 00094, in 2020.
Read side by side, the Văn Yên and Trà My files show two ways to define a cassia region. Văn Yên records both oil and cinnamaldehyde, a file tied to consistent quality across a large area. Trà My records a high oil content in the trunk bark, a file tied to the depth of each piece. Both are facts, not rankings.
The Trà My file names only the genus Cinnamomum, not the species. The detail looks administrative, but it explains why the name Trà My cassia cannot yet be translated into one single Latin name.
Cassia on skin: concentration limits
Cinnamaldehyde is one of the most tightly limited fragrance molecules. The library classifies it as a high risk skin sensitiser and a moderate fragrance allergen. IFRA limits cinnamaldehyde to 0.05 percent in leave on products. Under EU rules the label must name it above 10 ppm in leave on products, or 100 ppm in rinse off products.
From the molecule's limit, the library derives the oil's limit. For cassia oil the maximum dermal level is 0.05 percent, calculated on the assumption that the whole oil is cinnamaldehyde. For Ceylon cinnamon bark oil the figure is 0.07 percent, based on a cinnamaldehyde level of 75.7 percent. For Ceylon cinnamon leaf oil the limit comes from eugenol instead, and the figure is 0.6 percent.
Those numbers are very small in a real bottle. In 10 ml of carrier oil, 0.05 percent equals 0.005 ml, about one tenth of a drop at 20 drops per ml. Put another way, a single drop of cassia oil already exceeds the limit for a whole 10 ml bottle. Cassia in a body oil is a material to be weighed on a scale, not counted with a dropper.
The library adds further notes for both cassia and Ceylon cinnamon bark oil: contraindicated in pregnancy and breastfeeding, to be avoided on damaged or hypersensitive skin, avoided for children under 2, and an interaction with anticoagulant medication. Undiluted cinnamon bark oil is severely irritating; cases of severe burns in children have been reported from direct contact.
These limits do not remove cinnamon from perfumery. They only put it in its proper place: a warm, spicy line within a larger structure, in a small dose, calculated before pouring.
Two mountain regions, four geographical indication files, one molecule filling almost the whole bottle.
The name of cinnamon changes with the language. Cinnamaldehyde does not.
What remains is paperwork, the peeling season, and one tenth of a drop.