This is why I bike rather than run. Crashing is your primary risk there but otherwise, it's stupendously hard+ to hurt yourself unknowingly.

I'm not fully aware of all of the possible long term risks to cycling but I know pollution from cars comes up a lot. I believe the prevailing consensus is that the benefits still outweigh the harm done.

+: May be overstating it. You can hurt your wrists through a bad fit and your knees through using too high a gear. In both cases, your body will probably let you know about it soon though.