The head at the tip of a strike-anywhere match contains all the chemicals required to create a spark. A strike-anywhere match only needs to be rubbed against a surface with a high coefficient of friction, such as sandpaper, to create enough frictional heat to ignite the match. Safety matches differ from strike-anywhere matches since the chemicals necessary for ignition are divided between the match head and the treated strip found on the matchbox or matchbook. The friction between the match head and treated strip will ignite the match. Matches fail to ignite when wet because water reduces friction.