Match heads are made using phosphorus – a highly combustible element – that catches fire due to the friction caused when striking the match.
Safety matches are slightly different. They will only light if you strike them using the surface on the side of the box. In this case, the match head contains potassium chlorate – an accelerant that speeds up the reaction. The rough side of the box contains most of the phosphorus. Bring the two together and add the heat generated by friction, and you have a flame.
Waterproof matches have a thin coating of wax over the whole match. This is removed when striking the head against the box, exposing the phosphorus. This allows the match to catch.
To give you enough time to move the match to whatever you wish to light, most matchsticks are treated with paraffin (candle wax).
Fast Fact: The first friction match was invented in 1826 by English chemist, John Walker. The earliest match is thought to have arisen in China in 577 AD. These were nothing more than sticks impregnated with sulphur.