When you buy something using the retail links in our stories, we may earn a small commission. Outside does not accept money for editorial gear reviews. Read more about our policy. We’ve all been there: a couple miles into what was supposed to be a long outing on the trail, you feel the hot spot burning inside your shoe. A damn blister. Maybe you’re in ill-fitting new shoes or bunchy socks that caused your feet to sweat. Maybe you just have blister-prone feet. Either way, a skin bubble can put an end to an otherwise great day—or lead to some serious discomfort. Don’t despair: we called up John Vonhof, author of Fixing Your Feet: Injury Prevention and Treatments for Athletes ($20, Wilderness Press), first published in 1997 and now in its sixth edition. Vonhof is a former paramedic and an ultrarunner who now works the medical tents at races like California’s 100-mile Western States Endurance Run and the Badwater 135, as well as Decaman, a series of ten back-to-back Ironmans in New Orleans. He gave us his best advice on blister prevention and treatment. They always seem tiny and innocuous, but they can be day enders. “Even a blister the size of a pea in the wrong spot—at the base of...