A contact explosive is a chemical substance that explodes violently when it is exposed to a relatively small amount of energy (e.g. friction, pressure, sound, light). Though different contact explosives have varying amounts of energy sensitivity, they are all much more sensitive relative to other kinds of explosives. Contact explosives are a part of a group of explosives called primary explosives, which are also very sensitive to stimuli but not to the degree of contact explosives. The extreme sensitivity of contact explosives is due to either chemical composition, bond type, or structure.