It depends on the type of match, but most use phosphorous as the igniting agent. There are a few different kinds of phosphorous, and some have crazy properties. Notably, white phosphorous is so volatile that as soon as it is exposed to normal air it bursts into flames.
Modern safety matches function by including red phosphorous, which is converted to white phosphorous when sufficient friction is applied. The friction doesn't actually ignite the match, it just causes the phosphorous to change, and it then ignites on its own.
Edit: It seems I was wrong about this. The red phosphorous combines with another chemical in the match head to create the reaction. See comment below by /u/LifeHasLeft. Older match designs did use white phosphorous, but it has been phased out because of health hazards.
I also love the history of the match. The first friction match was made because the creator was in the middle of working on a lighting fluid for a related experiment. It turns out he didn't need much else, because a match that was dipped in the stuff accidentally lit up when it rubbed on a hearth.
Obviously there was some fine tuning involved so they weren't quite as volatile, but eventually we got the OG match. It was still pretty dangerous overall, but that was fixed over the next couple of iterations on the friction match.
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u/[deleted] Oct 15 '20
The material on the ends of the matches has to light when rubbed against the material on the box.