If your postmarathon blisters are not tense or extensive, just leave them be. At most, use ice water soaks. If your blisters have broken open, your primary goal is to prevent infection. Soak your feet twice a day for 10 to 20 minutes in water with providone iodine solution added (10:1 water to providone solution), then dry your feet and cover them with clean socks. Continue this care until the blistered areas are dry (not draining or oozing) and pain free. Self-care by opening an intact blister should be considered only for tense, painful blisters. In this case, clean the area with providone iodine solution, then open the blister near its edge with a clean instrument. The opening should be at least one-quarter-inch wide. After the blister is open, treat it the same way as a blister that broke open during the race.
If the area around the blister becomes more painful, or if there’s redness spreading from the site, suspect an infection. If a blister site becomes infected, the infection usually arises two to five days after the blister is exposed.
Seek professional care for extensive blisters, suspected infection, or tense painful blisters that you cannot care for yourself. It’s best to delay your return to running until blistered sites are pain free. Altering your stride to avoid painful areas can unduly stress another area and risk a new injury.