Are the shoes broken in? That's the easiest thing to check for...
Otherwise, the main cause for me was shoes that were too wide or too big. Shoes that are too big cause your feet to have a ton of extra movement within the shoe, causing lots of problems with blisters. And if they are too small, I would imagine your foot would get more friction than it should, too.
I got my feet fit for shoes at a walk/run specialty store and have never had a problem since they got me the right brand/width/size. But if I wear anything else...![]()