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Agarwood forms when an Aquilaria or Gyrinops tree is wounded and the wound is colonised by fungi and other microbes. The tree responds by producing a dark, fragrant defensive resin, rich in sesquiterpenes and 2-(2-phenylethyl)chromones, which slowly saturates the surrounding wood over months to years.
- An unwounded tree contains no agarwood, only pale, light, largely scentless wood.
- Fungi such as Fusarium and Lasiodiplodia are among those linked to resin formation.
- Plantations copy the process by wounding trees and inoculating them on purpose.
Agarwood is not part of a tree's normal anatomy. It is the product of a defence response, formed only after a tree in the genus Aquilaria or Gyrinops is wounded and then colonised by fungi and other microorganisms. Cut into a healthy, unwounded tree of either genus and there is no agarwood to find, just pale, lightweight, largely scentless wood. Everything that makes agarwood valuable, its density, colour and fragrance, is produced by the tree afterwards, as a reaction to injury.
This guide covers what the scientific literature establishes about that process: what triggers it, which organisms are involved, what compounds the tree produces, and how long formation takes. Grading and authenticity testing are covered separately in the Quality & Authenticity hub.
A healthy tree makes no agarwood
Aquilaria and Gyrinops are the two genera responsible for essentially all agarwood, both in the plant family Thymelaeaceae. Aquilaria has about 21 recognised species, depending on the classification used, and several are documented agarwood producers, including Aquilaria malaccensis, Aquilaria crassna and Aquilaria sinensis. Gyrinops has around nine species, with Gyrinops versteegii from Indonesia and Gyrinops walla from Sri Lanka among the most studied in agarwood research.
In an unwounded tree, the wood these species produce is unremarkable: pale, low in density and without the resinous fragrance agarwood is known for. There is no reservoir of fragrant resin waiting inside the tree to be tapped. The resin only appears after the tree is damaged and responds to that damage, which is also why agarwood cannot be obtained simply by felling any tree of the right species.
What triggers resin formation
The process begins with physical injury: lightning, storm damage, insect boring, animal damage, or a cut made by a person. A wound on its own is not enough. What turns an ordinary wound into agarwood is colonisation of the injured tissue by fungi and other microorganisms, which the tree responds to by producing and depositing resin around the site of infection.
Researchers describe this as a stress response. The tree generates aromatic compounds as a defence intended to wall off and resist the spreading infection, broadly similar to how many trees produce resin or gum in response to injury and disease. Over months and years this resin accumulates and saturates the surrounding heartwood, gradually darkening it from pale towards brown, and in the most saturated wood, towards black.
Want to know what this slow, uneven biology means for what agarwood costs?
Why is agarwood so expensive?The fungi and microbes involved
A number of fungal genera have been identified in connection with agarwood formation, including Fusarium, Lasiodiplodia, Penicillium and Aspergillus. Many of the fungi involved are endophytes, organisms that live inside plant tissue without necessarily causing disease on their own, and several studies have also found bacteria present alongside fungi in resinating wood.
This is the scientific basis for most modern agarwood cultivation. Plantation growers deliberately wound trees and, in many operations, inoculate the wound with cultured fungi, commonly Fusarium species, to trigger the same defensive response under controlled conditions rather than waiting for it to happen by chance.
The chemistry behind the scent
The resin that accumulates in the wood is made up mainly of two classes of compound: sesquiterpenes and 2-(2-phenylethyl)chromones, usually shortened to chromones. The balance between them varies by species, by how the agarwood formed, and by study.
Sesquiterpenes are a large family of compounds built from linked isoprene units, and they account for much of agarwood's layered aroma. Chromones are increasingly studied for biological activity beyond fragrance, including antimicrobial and anti-inflammatory effects observed in laboratory research. That research is at an early stage and is not a basis for health claims about burning or wearing agarwood.
How long formation takes
There is no single fixed timeline for agarwood formation. Wild agarwood, formed through chance injury and natural colonisation, is generally understood to take years to decades before resin accumulates enough to produce dense, high resin heartwood. Induced agarwood, formed through deliberate wounding and inoculation on plantation trees, can produce harvestable resin considerably sooner. Research trials have assessed resin at intervals such as six months, one year and two years after inoculation, with resin content and quality continuing to develop over longer periods.
This difference in timeline is one of the main reasons wild and plantation agarwood are not treated as equivalent in the trade, covered in our guide to wild vs plantation agarwood.
Why this biology makes genuine agarwood rare
Three facts about the process explain much of agarwood's price. First, it cannot be produced instantly. Even accelerated plantation methods need months to years of resin accumulation, and the material associated with old wild trees reflects a far longer timeline. Second, not every wounded tree responds the same way. Resin yield and quality vary considerably between individual trees, even of the same species in similar conditions, for reasons researchers are still working to characterise. Third, resin forms only where infection spreads, so a single tree often yields a limited amount of high resin wood, concentrated around the original wound and surrounded by wood that never converted.
This is also part of why misrepresentation is so common, a problem covered in fake oud: what to look for. The biology is slow and uneven, but demand for abundant high grade material is not, which creates an obvious incentive for synthetic substitutes and inflated claims.
Wild wounds vs deliberate induction
All agarwood relies on the same underlying biology: wounding, then microbial colonisation, then resin deposition. What differs is how the wound and infection happen. Wild agarwood results from injuries and colonisation that occur by chance over the natural life of a forest tree, often over a long period and frequently in older trees. Plantation agarwood results from growers deliberately wounding cultivated trees and, in most modern operations, inoculating them with selected fungal strains or other inducing agents to trigger the same response on a predictable schedule.
Whether that difference produces a meaningfully different scent and quality is a genuinely debated question among collectors and traders, covered in full in wild vs plantation agarwood.
How we checked this. This guide describes the broad mechanism reported across agarwood research. Where studies disagree on proportions or timelines, we say so rather than picking one figure.