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Tiếng Việt

Learn · Part Three — Learning origins · Lesson 12 of 13

Three scented woods sold for the car: what you are actually smelling

The three names on bags of scented wood for the car belong to three different trees. One smells of almost a single compound; two are rare, protected species.

Search for "scented wood for the car" in Vietnam and most of what comes up is bags of wood shavings sold under three names: xá xị, hoàng đàn and bách xanh. The three names belong to three quite different trees with three different smells, and two of the three are rare species protected by law. This lesson explains where each smell comes from, and why the name on the bag is not enough to tell you what you are holding.

Xá xị: almost a single compound

The xá xị tree (Cinnamomum parthenoxylon) belongs to the same genus as cinnamon and camphor. A 1995 study analysed the wood oil of trees from several regions of Vietnam and found safrole made up about 90% of it. Almost the whole smell of the wood is one molecule.

Safrole smells sweet and warm, close to candy and liquorice. Americans know it from root beer, a soft drink once flavoured with the root of the sassafras tree — also rich in safrole — until the US Food and Drug Administration banned safrole in food from 1960.

That ban had a reason. At high doses safrole causes liver tumours in rodents, and the US National Toxicology Program lists it as reasonably anticipated to be a human carcinogen, based on animal studies. Those studies fed high doses; they did not involve breathing the smell of a bag of wood, and no study has measured the risk of hanging xá xị wood in a car. But a closed cabin at up to 60 °C, sat in every day, is exactly the kind of repeated exposure worth avoiding when you have a choice.

Safrole is also a precursor for making the drug MDMA, which puts it in Table I of the 1988 United Nations Convention against Illicit Traffic in Narcotic Drugs. That demand has driven illegal felling of these trees in the Cardamom Mountains of Cambodia.

Hoàng đàn: a name bigger than the tree

Vietnam's own hoàng đàn (Cupressus tonkinensis) grows on limestone hills in Huu Lung, Lang Son province. Surveys between 2004 and 2009 found only 25 trees, and the species has been proposed as Critically Endangered. Its wood and roots were exploited so heavily for their oil that people used explosives to reach old roots wedged in the rock. Since 1997 there has been no hoàng đàn timber in commercial quantities.

So a bag of "hoàng đàn" today is very unlikely to be genuine Lang Son hoàng đàn. Oil sold internationally under the name usually comes from the Himalayan cypress, Cupressus torulosa — the related species whose botanical name our page for this oil states plainly.

Bách xanh: precious, fragrant, and not yet well read

Bách xanh (Calocedrus macrolepis) gives a fragrant, durable wood used for fine furniture and incense. It has been heavily logged for its timber and is on Vietnam's list of rare plants whose harvesting is restricted.

On its smell, the data is thin. Published analyses of bách xanh oil differ by plant part and collection area, and are not enough to say which compounds make the scent of the wood. Under the site's data standard, where something is uncertain we leave it blank rather than guess.

The name on the bag is not evidence

  1. Wood shavings carry no species name. By eye you cannot tell xá xị from camphor wood, or from any wood soaked in essential oil. Only an analysis, or a seller who can prove where the wood came from, can answer that.
  2. The stronger the smell, the more worth asking. A bag of wood that still smells strong after many months may have been topped up with oil. That is not wrong, but it should be stated on the label.
  3. Two of the three are protected trees. Buying their wood without a known source feeds the very harvesting that has pushed them to the edge of extinction.

Our scented wood takes the opposite approach

A base wood with almost no smell of its own, impregnated with one essential oil that has a botanical name and a lot number, with the GC/MS analysis of that lot published unedited. Then the name on the label can be checked. See hanging scented wood for the car.

Sources

  • Constituents of the essential oils of Cinnamomum parthenoxylon (Jack) Nees from Vietnam. Journal of Essential Oil Research 7(1), 1995.
  • US National Toxicology Program. Report on Carcinogens: Safrole.
  • Royal Botanic Garden Edinburgh. Threatened Conifers of the World: Cupressus tonkinensis; Calocedrus macrolepis.
  • United Nations Convention against Illicit Traffic in Narcotic Drugs and Psychotropic Substances (1988), Table I.

Further reading for this part

A shared list for the whole of Part Three — Learning origins, not a note for every sentence. We state what each source was used for.

  1. Young Soo Joung and Cullen R. Buie, 2015. Aerosol generation by raindrop impact on soil The MIT study that filmed how raindrops fling up bubbles carrying material from the soil into the air. It underpins the explanation of the smell of first rain: rain does not create the smell, it spreads it.
  2. Cây cỏ Việt Nam The botanical identification source for the species in the dictionary. Used together with Những cây thuốc và vị thuốc Việt Nam, and we say so when the two record things differently.

One thing must be said plainly. We have not read every work above in the original; most of the knowledge comes through secondary literature and reviews. We say so rather than let the list suggest a depth of research we have not reached.

Last updated: October 2026