The prized oil is only extracted from the darkened heartwood of those trees which have been infected by a particular type of fungus or mold known as phialophora parasitic. In uninfected trees, the heartwood, or center of the tree, is odorless and relatively light and pale in color. Infected tree, however, has a dark, very dense, resin embedded heart which occurs as a natural defense mechanism by the tree itself where it produces the resin in response to the attack. The fungus and tree have a battle of sorts with the decomposition process continuing over time and in the process generating a very rich and dark resin that resides within the heartwood. The very valuable agarwood develops slowly over time, typically several hundred years or more. That resin embedded wood is the prize for those seeking to make essential oils, perfumes, or incense. Because of its rarity, Agarwood oil is not well known in the West, except by connoisseurs of essential oils and very experienced practitioners of aromatherapy.