Resin is probably one of the most under-appreciated raw materials in nature. The vast majority of resins are produced by plants (one rare exception is propolis, which is made by bees). It is a complex substance whose purpose in life is to act as a protective response to injury of the plant by insects and other physical damage. In the human world, it has a wide variety of uses, depending on its chemical composition. Resins have been used as medicine, adhesives, food product stabilizers, wood preservatives, incense, perfume, and insect repellents, among others.