1. Clean the blister
Gently clean the blister with soap and water, then wipe the blister and surrounding area with isopropyl (rubbing) alcohol.
2. Drain the blister
Heat a needle over a flame until the tip is glowing red. Let the needle cool without touching anything else. Poke a hole in the base of the blister to allow the fluid inside to drain. Press lightly on the blister to help drain it.
3. Dress the blister
Dab a little antibiotic ointment on the drained blister and cover it with a bandage.
Tips:
1. Don't get burned holding the needle over the flame. Use a pair of pliers, hot pad or cloth to hold it. You don't want to create a burn blister while trying to fix a friction blister.
2. If you must continue the activity that caused the blister, whether you choose to drain it or not, cut a piece of moleskin like a donut with a hole in the middle. Put the moleskin around the blister. This helps keep pressure off the blister, which should minimize any further injury. If you've drained it, then cover the whole thing with a bandage.