In ancient times, frankincense was used by upper-class Egyptians to ward off foul odors, which were associated with evil. It is still burned as incense today but needs an outside heat source, such as incense charcoal, to burn. Frankincense is an oleo-gum-resin that seeps from the tree when the bark is injured or cut. The liquid solidifies on contact with air into globular chunks or "tears." When ground, frankincense powder quickly hardens again upon air exposure. The resinous, dry and balsamic aroma is a component of many perfumes.