I got a chronic saddle sore (had to have it injected with cortisone by a dermatologist finally) from, I am almost positive, riding a too-narrow saddle that rubbed me in the wrong place right along the outer edge. I finally figured out that I wasn't balanced on my sit bones but riding right on the inner edge of them. The dratted sore didn't go away in months of not riding! It was kind of a boil, but filled with blood instead of mucus. Nasty. Switching (back) to a Terry Butterfly saddle ended up being the final cure, as it started re-appearing (even after the cortisone shot) right after I started riding on the narrower saddle again. I get some occasional chafing from the Butterfly on longer, sweatier rides, but that's a small price to pay compared to an actual saddle sore.