Wax is a highly flammable substance. Wax is the fuel that keeps candles burning so that they produce light. The wick soaks up the wax and draws more into the flame so that it stays lit.
According to HowStuffWorks, wax is a petroleum product that is formed out of crude oil. Crude oil is the same natural substance from which gasoline and kerosene are produced. In addition to candles, wax is used as a fuel in manufactured fireplace logs and fire starters. In those applications, the wax is mixed with another flammable substance, such as sawdust, cotton fibers or newspaper. Because wax is very flammable, precautions are necessary when melting it in a home environment. Wax should be melted slowly in a double boiler to avoid fires.