Match heads are made of different chemicals. The main ingredients are potassium chlorate, sulfur and glass. There is no phosphorus in the head of the matchstick. The main purpose of the sand and glass on both sides of the box is to generate heat through friction. This amount of heat converts red phosphorus into white phosphorus. White phosphorus is incredibly pyrophoric. It can ignite in the presence of oxygen in the air, or in the presence of potassium chlorate itself. Sulfur (along with oxygen) burns flames. The wooden stick of matches works the rest.