Incense is composed of aromatic plant materials, often combined with essential oils. Incense can generally be separated into two main types: "indirect-burning" and "direct-burning." Indirect-burning incense (or "non-combustible incense") is not capable of burning on its own, and requires a separate heat source. Direct-burning incense (or "combustible incense") is lit directly by a flame and then fanned or blown out, leaving a glowing ember that smoulders and releases fragrance.