Agarwood or aloeswood is a fragrant dark resinous wood used in incense and perfume. It is formed in the heartwood of aquilaria trees when they become infected with a type of mould. Prior to infection, the heartwood is odourless, relatively light and pale coloured; however, as the infection progresses, the tree produces a dark aromatic resin, called aloes or agar (as well as gaharu, jinko, oud, or oodh; not to be confused with bukhoor), in response to the attack, which results in a very dense, dark, resin embedded heartwood. The resin embedded wood is valued in many cultures for its distinctive fragrance, and thus is used for incense and perfumes. The composition of agarwood oil is exceedingly complex with more than 150 compounds identified so far. At least 70 of these are terpenoids which come in the form of sesquiterpenes and chromones; no monoterpenes have been detected at all. Other common classes of compoundsinclude agarofurans, cadinanes, eudesmanes, valencanes and eremophilanes, guaianes, prezizanes, vetispiranes, simple volatile aromatic compounds as well as a range of miscellaneous compounds. The exact balance of these materials will vary depending on the age and species of tree as well as the exact details of the oil extraction process.