There's a lot of dubious assertions in the answers here, and frankly some bad advice regarding how long to wait before treating a blister. We just had a lecture on blister management in my WFR class yesterday, so I'll give this a go.
The answer to "should I deflate this blister" comes down to a very simple question: Will it pop itself if I don't? Any blister on the foot is likely going to pop itself if you don't. Blisters in other locations (typically the hands) may be less likely to.
- It's always preferable to deflate a blister under (relatively) clean and controlled conditions, rather than let it pop itself.
- A blister that pops itself is more likely to get infected, and more likely to spread pus around and infect other areas.
- An untreated blister or hotspot will grow larger.
It's important to understand why blisters form. Friction causes heat to build up in an area, and the body creates a blister to protect the underlying skin from this excessive heat. If you don't reduce the friction, the blister will worsen.
The first thing you want to do is treat any hotspot before it becomes a blister. When a blister first starts to form, before it is pus-filled, is the optimal time to treat it. Clean and dry the area, then cover it in athletic tape. When possible, wrap the tape all the way around whatever body part is blistered, so the tape adheres to itself and you aren't just relying on the tape sticking to sweaty skin. The tape is there both to cover the hotspot, and also to provide a lower-friction surface to prevent further damage from occurring. You should also readjust your footwear/gloves if possible to reduce that friction.
If a blister does form, time is of the essence. The long you wait, the larger the blister will grow, because that heat is still being applied. This is why you should not wait until they end of the day to treat your blisters – treat all blisters ASAP! If the blister is relatively small and in an area where you can simply stop causing friction, then you don't need to deflate it. This is likely only going to be practical for some hand blisters; foot blisters usually need to be popped.
To pop the blister:
- Wash your hands first.
- Wash the area on and around the blister with soap/water, iodine solution, or rubbing alcohol, and allow to dry. This will reduce the likelihood of introducing bacteria.
- Sterilize a needle, safety pin, or similar object over an open flame; or, use a packaged sterile needle if you have one available.
- Stab the base of the blister in a couple places, then gently press to deflate. Be mindful of where the pus drains to.
- Leave the skin in place.
- If you have moleskin, 2nd skin, etc. make a donut-shaped cutout to encircle the blister but not cover it.
- Fill the donut hole with 2nd skin, antibiotic ointment, etc. if available. A bit of sterile gauze with iodine on it is an acceptable alternative. This is mostly to prevent infection and cover the blister site.
- Cover the entire area with medical tape. Consider what motion was causing the blister to form, and try to apply the tape in such a way that the motion will not strip it off. When possible, wrap the tape around whatever body part the blister is on, so the tape can stick to itself and not just the skin.
- Inspect the blister at least every 6 hours! If you don't inspect the blister and replace the dressing, it may get worse without you noticing. Leave the donut in place, but replace the dressing in the donut hole and the surrounding tape.