Agarwood, also known as oud, oodh or agar, is a dark resinousheartwood that forms in Aquilaria and Gyrinops trees (large evergreens native to southeast Asia) when they become infected with a type of mould. Prior to infection, the heartwood is relatively light and pale coloured; however, as the infection progresses, the tree produces a dark aromatic resin in response to the attack, which results in a very dense, dark, resin embedded heartwood. The resin embedded wood is commonly called gaharu, jinko, aloeswood, agarwood, or oud (not to be confused with 'Bakhoor') and is valued in many cultures for its distinctive fragrance, and thus is used for incense and perfumes.
The odour of agarwood is complex and pleasing, with few or no similar natural analogues. As a result, agarwood and its essential oil gained great cultural and religious significance in ancient civilizations around the world, being mentioned throughout one of the world's oldest written texts – the Sanskrit Vedas from India.
As early as the third century AD in ancient China, the chronicleNan zhou yi wu zhi (Strange things from the South) written by Wa Zhen of the Eastern Wu Dynasty mentioned agarwood produced in the Rinan commandery, now Central Vietnam, and how people collected it in the mountains.
Agarwood’s use as a medicinal product has been recorded in the Sahih Muslim, which dates back to approximately the eighth century, and in the Ayurvedic medicinal text the Susruta Samhita.
Starting in 1580 after Nguyễn Hoàng took control over the central provinces of modern Vietnam, he encouraged trade with other countries, specifically China and Japan. Agarwood was exported in three varieties: Calambac (kỳ nam in Vietnamese), trầm hương (very similar but slightly harder and slightly more abundant), and agarwood proper. A pound of Calambac bought in Hội An for 15 taels could be sold in Nagasaki for 600 taels. The Nguyễn Lords soon established a Royal Monopoly over the sale of Calambac. This monopoly helped fund the Nguyễn state finances during the early years of the Nguyen rule.
Xuanzang's travelogues and the Harshacharita, written in seventh century AD in Northern India, mentions use of agarwood products such as 'Xasipat' (writing-material) and 'aloe-oil' in ancient Assam (Kamarupa). The tradition of making writing materials from its bark still exists in Assam.
Aquilaria tree showing darker agarwood. Poachers had scraped off the bark to allow the tree to become infected by the ascomycetous mould.
Agarwood is known under many names in different cultures:
In Urdu (Pakistan) and Hindi (India), it is known as agar, which is originally Sanskrit aguru (in Bengali, also aguru).
In Bangla (Bangladesh) agarwood known as "agar gaach (আগর গাছ)" and the agarwood oil as "agar attar (আগর আতর)".
It is known by the same Sanskrit name in Telugu and Kannada as Aguru.
It is known as chénxiāng (沉香) in Chinese, "Cham Heong" in Cantonese, trầm hương in Vietnamese, and jinkō (沈香) in Japanese; all meaning "sinking incense" and alluding to its high density. In Japan, there are several grades of jinkō, the highest of which is known as kyara (伽羅).
Both agarwood and its resin distillate/extracts are known as oud (عود) in Arabic (literally "rod/stick") and used to describe agarwood in nations and areas in Arabic countries. Western perfumers may also use agarwood essential oil under the name "oud" or "oudh".
In Europe it was referred to as Lignum aquila (eagle-wood) or Agilawood, because of the similarity in sound of agila to gaharu.
Another name is Lignum aloes or Aloeswood. This is potentially confusing, since a genus Aloe exists (unrelated), which has medicinal uses.
In Tibetan it is known as ཨ་ག་རུ་ (a-ga-ru). There are several varieties used in Tibetan Medicine: unique eaglewood: ཨར་བ་ཞིག་ (ar-ba-zhig); yellow eaglewood: ཨ་ག་རུ་སེར་པོ་ (a-ga-ru ser-po), white eaglewood: ཨར་སྐྱ་ (ar-skya), and black eaglewood: ཨར་ནག་(ar-nag).
In Sri Lanka it is known as "Walla Patta" වල්ලා පට්ටා
There are seventeen species in the genus Aquilaria and eight are known to produce agarwood. In theory agarwood can be produced from all members; however, until recently it was primarily produced from A. malaccensis. A. agallocha and A. secundaria are synonyms for A. malaccensis.A. crassna and A. sinensis are the other two members of the genus that are usually harvested.
Formation of agarwood occurs in the trunk and roots of trees that have been infected by a parasitc ascomycetous mould, Phaeoacremonium parasitica, a dematiaceous (dark-walled) fungus. As a response, the tree produces a resin high in volatile organic compounds that aids in suppressing or retarding the fungal growth, a process called tylosis. While the unaffected wood of the tree is relatively light in colour, the resin dramatically increases the mass and density of the affected wood, changing its colour from a pale beige to dark brown or black. In natural forest only about 7% of the trees are infected by the fungus. A common method in artificial forestry is to inoculate all the trees with the fungus. Oud oil can be distilled from agarwood using steam, the total yield of agarwood (Oud) oil for 70 kg of wood will not exceed 20 ml (Harris, 1995).
The First International Scientific Symposium on Agarwood was held at the Faculty of Forestry, Universiti Putra Malaysia, during 2013 under the auspices of Associate Professor Dr. Rozi Mohamed 
Overharvesting and habitat loss threatens some populations of agarwood-producing species. Concern over the impact of the global demand for agarwood has thus led to the inclusion of the main taxa on CITES Appendix II, which requires that international trade in agarwood is subject to controls designed to ensure that harvest and exports are not to the detriment of the survival of the species in the wild.
In addition, agarwood plantations have been established in a number of countries, and reintroduced into countries such as Sri Lanka as commercial plantation crops. The success of these plantation depends on the stimulation of agarwood production in the trees. Numerous inoculation techniques have been developed, with varying degrees of success.
^ abcYule, Henry and Burnell, Auther Coke (1903) "Eaglewood" Hobson-Jobson: A Glossary of Colloquial Anglo-Indian words and Phrases, and of Kindred Terms, Etymological, Historical, Geographical and Discursive (2nd edition) John Murray, London, p. 335, OCLC33186146
^Parfionovitch, Yuri; Dorje, Gyurme and Meyer, Fernand (1992) Tibetan medical paintings: illustrations to the Blue beryl treatise of Sangye Gyamtso (1653–1705) (English edition of Tibetan text & paintings) (2 volumes) Serindia, London, ISBN 0-906026-26-1
^Aromatics, an encyclopedia. 2010. Please note: due to the method of assigning names to medicinal botanicals used in Tibet, it must be considered that woods with similar medicinal properties are named as varieties of the same medicine, and not according to anything akin to the nomenclature of Western botany. Tibetan botanical taxonomy is still in the earliest stage: "white aloeswood" actually refers to the non-aromatic portions of the Indian sandalwood tree; "yellow aloeswood" refers to the scented heartwood of Santalum album. Unique aloeswood is the highest grade of Aquilaria agallocha resin, known in English as Agallochum, while "black aloeswood" is the resin infused wood of the same tree; "brown aloeswood" is actually the scented wood of several Dalbergia species from India and Bhutan.
^ abcdNg, L.T., Chang Y.S. and Kadir, A.A. (1997). "A review on agar (gaharu) producing Aquilaria species". Journal of Tropical Forest Products2 (2): 272–285.
^formerly Phialophora parasitica: Crous, P. W.; Gams, Walter; Wingfield, Michael J.; Van Wyk, P. S. (1996). "Phaeoacremonium gen. nov. associated with wilt and decline diseases of woody hosts and human infections". Mycologia88 (5): 786–796. doi:10.2307/3760973. JSTOR3760973.