Marathon Blister. Should I pop it?

Question:
Hi MyRunningDoc!


I have been reading your site. This blister formed on my heel yesterday. It is huge and painful. I am running in the Avenue of the Giants Marathon on May 5, 2013 and really can't take a break from marathon training. Should I pop it?

Thanks!
W.H., San Francisco CA

Answer:
Thank you for your inquiry! That is certainly a Giant of a marathon blister. I can see how that would hurt and put a damper on your final marathon training.

There is always an advantage and a disadvantage to draining in any blister on the foot that pops up during training.

With a blister that large and a marathon that close, it is unlikely that you would be able to run the marathon without significant pain. In fact the blister is so big it would probably pop during the marathon anyway.

With most small blisters, it is typically better to let them go away on their own. If you do not drain a small blister and can keep it from getting rubbed when you are running, the fluid will gradually recede and the blister will re-adhere. It will eventually peel away revealing healthy skin underneath. It is also the least likely to get infected because you don't open the blister allowing bacteria to get inside the skin.  This actually will heal the fastest and is the safest approach.

Things get tricky when a running blister on the foot gets big.

When you have a big running blister that causes a great deal of discomfort when you run, it actually hurts because the fluid is getting pushed and compressed.  If you step on a water balloon, the balloon will squish outward under your foot. The balloon will push out and stretch as far as it can unless it pops.

So when you run on a blister like this one pictured here, the blister fluid actually pushes and continues to separate the layers of skin at the edge of the blister. This of course causes more irritation and more fluid accumulation, making the blister even bigger as you continue to run.  The only way to stop this process is to stop irritating the blister on the foot. One way to do this of course is to stop running.

If you can pad the blister and keep the pressure off of it you might be able to continue training without the blister getting any bigger.  That would be hard to do given the location of this blister on the inside of the foot and heel. It will be almost impossible to remove all the pressure from the heel inside the running shoe.

If you pop the blister, it will hurt more for the first day or two.  You can decrease the amount of discomfort by using moleskin or another type of blister cover that will stop the friction from rubbing the overlying skin. It may also be helpful to put some padding around the blister in order to decrease irritation.

If you decide to pop your blister, it is always best to drain the blister by making a small hole at the bottom edge of the blister down toward the bottom of the foot so that the fluid will continue to drain downward and out of the blister as it re-accumulates. Typically some more blister fluid will accumulate inside the blister for several days after you pop it.

The skin on the top of the blister is not what is painful. It is the skin underneath. Some people start to drain the blister and realize this and then trim off the entire top of the blister. If you are to do that in this case, it would leave an open sore about the size of a half dollar. This would of course leave an enormous raw spot that would be very painful whenever you run during training. You foot would be killing you during the marathon.

In these types of cases it is often better to simply drain the blister and leave the top of the blister intact to function as a biologic dressing. This will take slightly longer to heal than if you don't drain the blister.  However this assumes that you are of course going to continue to run, train and complete the marathon that you have planned.

It would be best to be evaluated in person or by a podiatrist or arrange a remote consultation with a running injury expert in order to get more detail, before making your final decision.  You can also learn more about blisters from running by clicking here.

Dr. Christopher Segler, DPM a marathon runner, podiatrist and 10-time Ironman Triathlon finisher who is is Board Certified, American Board of Podiatric Medicine.  He believes the best podiatry practice combines cutting edge technology with the old-school convenience of house calls. He makes podiatry house calls for runners in San Francisco, CA and Houston ,TX. He also does remote consults for runners who live outside of the United States. If you have a question, you can reach him directly at 415-308-0833. You can learn more about running injuries at www.DocOnTheRun.com