What is oud — and why does it come from a wounded tree?

The short answer is this: oud is not a wood. It is a resin — a defence response produced inside an Aquilaria tree when the tree is infected by a specific fungal pathogen. The tree is, under ordinary circumstances, unremarkable. Pale heartwood, no particular scent. What transforms it is injury and infection, and the slow chemistry that follows.

The longer answer is why a tree's wound response produces the most expensive aromatic raw material in the world, why Hojai in Assam sits at the centre of India's finest agarwood supply, and why oud in a candle behaves differently from oud in perfume.

The biology: a defence mechanism made visible

Aquilaria trees are native to South and Southeast Asia — across a range that covers Assam, Bangladesh, Myanmar, Vietnam, and parts of the Malay archipelago. The species most relevant to Indian oud is Aquilaria malaccensis, also catalogued as A. agallocha. It grows to fifteen metres or more, typically in humid subtropical forest. In its healthy state, the heartwood is white to pale yellow and contains no aromatic compounds of note.

When the tree is wounded — by an insect, a physical injury, or by deliberate inoculation — the damaged tissue becomes vulnerable to fungal infection. The primary pathogen associated with agarwood formation is Phialophora parasitica, though several other fungal species (including members of the genera Fusarium and Aspergillus) have been identified in infected samples. The tree responds to the infection by producing a dense, dark resin — a phenolic compound matrix — in the cells surrounding the infected tissue. This is the agarwood.

The resin accumulates slowly over years, sometimes decades. It saturates the heartwood in layers, darkening it from pale to amber to near-black. The concentration determines the grade: low-grade agarwood may contain only 10–15% resin by weight; the highest grades are so resin-saturated they sink in water. The aromatic compounds responsible for oud's distinctive profile — sesquiterpenes including agarospirol, jinkohol, and guaiol — develop within this resin matrix, not in the wood itself.

Only a fraction of Aquilaria trees ever become infected. Of those that do, only a fraction produce resin at a concentration worth distilling. This is the first reason oud is what it is.

Why Hojai — the geography and the species

Hojai district sits in the Brahmaputra valley of Assam, in the foothills east of Guwahati. The climate is humid subtropical — heavy monsoon, high soil moisture, year-round warm temperatures. These are the conditions under which Aquilaria malaccensis thrives and under which fungal infection pressures are high enough to drive resin formation at scale.

A. malaccensis from this region is classified among the highest-grade agarwood species globally. The aromatic profile of Assam oud — the dark leather opening, the warm resinous middle, the persistent wood base — is specific to this species and this geography. Oud from Cambodia (A. crassna) or from the Arabian peninsula (typically Hindi-grade material, sometimes blended from South and Southeast Asian sources) has a markedly different character. The sesquiterpene ratios differ by origin, just as the terpene ratios in wine differ by terroir.

Hojai has been a centre of agarwood trade for generations. The distillers and growers here have both the species and the accumulated knowledge of managing it. Wild Aquilaria malaccensis is listed on CITES Appendix II — meaning international commercial trade in wild-harvested material is restricted and requires documentation. What this means in practice is that commercially available Indian oud now comes almost entirely from managed plantations. Hojai has an established plantation culture, and the supply chain from plantation to distillery is documentable. We source only from plantation-grown material.

The distillation: 24–48 hours for a fraction of a litre

Harvested agarwood heartwood is chipped — broken into small pieces that maximise surface area — then soaked in water for anywhere from several days to several weeks before distillation. The soaking opens the resin matrix and improves oil release. The chips then go into a still for hydro-distillation or steam distillation; the choice of method varies by distillery, but both are slow processes. A batch runs for 24 to 48 hours. The distillate — aromatic steam condensed into water plus oil — is separated, and the oud essential oil is collected from the surface.

The yield is extremely low. Quality Assam agarwood produces roughly 2 to 4 millilitres of essential oil per kilogram of infected heartwood — and this is for wood with a reasonable resin concentration. Lower-grade material yields less. The arithmetic is what it is: it takes a large quantity of slow-grown, slow-infected, carefully harvested wood to produce a small quantity of oil. This is why quality Assam oud trades reliably at ₹1,50,000 to ₹5,00,000 per kilogram. It is among the most expensive aromatic raw materials in the world, without qualification.

The scent: how it moves

Hojai oud opens with smoke and dark leather — the most immediately legible characteristic of Indian agarwood. This is not a delicate or ambiguous opening. It arrives clearly. Beneath it, within the first fifteen minutes, the resinous middle begins to emerge: warm, dense, animalic in the way that aged wood with a biological history always is. The base is deep wood with a slow sweetness that builds rather than fades — a quality specific to high-sesquiterpene agarwood oils, where the heaviest aromatic compounds are also the ones with the most structural complexity.

What makes oud unusual as an aromatic material is how far it travels across a single burn or application. Most fragrances exhaust their progression in the first hour. A quality oud is meaningfully different at hour one, hour two, and hour three. The scent profile at the end of a burn is not a diminished version of the opening — it is a different register of the same material.

Oud in a candle — different from oud in perfume

The mechanism matters. In perfume applied to skin, body heat provides a gentle, sustained diffusion. Lighter molecules — those with lower molecular weight and higher vapour pressure — volatilise first. Heavier molecules follow progressively over hours, which is why fragrances are described in terms of top, middle, and base notes. The progression is slow because skin temperature is slow and consistent.

A candle flame is different. The heat at the wax pool surface — the melt pool — is significantly higher and more concentrated than skin warmth. This means lighter molecules volatilise faster and more intensely than they would from skin. The smoky, leathery top notes of Hojai oud appear more immediately in a candle environment. More notably, the base notes — the heavy sesquiterpenes responsible for oud's deep wood character — are less immediately volatile and persist longest in the room as the lighter compounds burn off. A room that has had an oud candle burning for two hours retains the base character long after the flame is out. Skin does not hold fragrance the same way.

This is not a deficiency of the candle format. It is a different kind of experience from the same material.

Why we source from Hojai and not a fragrance supplier

Synthetic oud is built from a small number of isolated agarwood sesquiterpenes — agarospirol, jinkohol, and a handful of others — at concentrations calibrated to approximate the overall profile. What synthetic oud cannot replicate is the full sesquiterpene matrix of a genuine agarwood distillate: the several hundred minor aromatic compounds present in concentrations too small to synthesise economically but large enough to register as the difference between something that smells like oud and something that is oud.

This is the same molecular argument as with Kannauj rose attar versus synthetic rose fragrance. The gap is not primarily in the dominant compounds. It is in the supporting structure — the trace compounds that give genuine material its texture and its evolution over time. That is why we source directly from Hojai, and why we note the geography on every candle.