Are horse flies dangerous

Well, I'm not really positive if they can do any MAJOR damage, but my friend and i can't go on a walk without getting attacked by a swarm of horse flies. We run and in return they follow. Just the other night we went out and had to run all the way home because of them (that's about mile) And i don't mean jogging! I mean sprinting! And yet we STILL managed to get bitten! If anyone can help our predicament please tell us how to get rid of these bothersome pests! ^.^