He explains that unlike sandalwood incense, which is made from a naturally fragrant wood, agarwood isn't simply the wood of a certain kind of tree. Rather, agarwood is taken from the heartwood of Aquilaria trees after they produce a resin in response to an infection of mold.
施起燻表示，與檀香（由天然香木製成）不同，沉香並不是一種木材，而是從一種特殊香樹上，混合了油脂（樹脂）和木質成分，所「結」出來的固態凝聚物（稱為「沉」）。