San Francisco Podiatry Video


Friday, April 16, 2010

To Pop or Not To Pop: Blister treatment for runners explained by San Francisco's Running Podiatrist

Dr. Oz recently ran a segment on his television show instructing his audience to pop blisters whenever they occur on the feet. He went on to explain that if you successfully get all of the fluid out, the top layer of the blister will form a adhere down to the tissue underneath and create a "biologic dressing."

While this may be sound advice for a typical healthy woman who gets a blister from a new pair of high heels, the real question for Bay Area runners is: "Should I drain a blister" if I am a runner training for a race such as a marathon or triathlon?

The best answer is "sometimes you should, and sometimes you shouldn't."

The medical term for the type of blisters on the feet when running are "friction blisters." Blisters on the feet occur from a combination of skin friction and pressure. When your foot slides around inside the running shoe, you get friction. Rubbing the skin over and over in one spot (such as the back of the heel or ball of the foot) causes the layers of the skin to begin to separate. Fluid then seeps into this newly created space between the layers forming the blister.

Keep irritating the area and the blister continues to get bigger. Even if you simply continue to apply pressure to the blister (like pressing it against the heel counter inside the running shoe) it will continue to get bigger. This is because the fluid will try to spread outward and keep separating the skin layers. Then even more fluid seeps in to make the blister bigger.

If you keep rubbing the blister long enough, the skin on the top of the blister will tear effectively popping on its own. The blister then starts to ooze relieving the pressure as the fluid leaks out. So should you take charge and drain it yourself?

What sports medicine podiatrists know about blisters in runners is:

1) small non-painful blisters heal quickly
2) large painful blisters hurt less if drained and not irritated, but hurt more and have a slightly higher risk of getting infected if they are drained and the activity (such as running) is continued
3) blisters with the overlying blister roof removed will heal, but hurt more initially

So If you are runner with a small blister on a toe and it doesn't hurt don't drain it. It will heal quickly and has a very low risk of infection. If the fluid can't drain out, bacteria can't get in. If you have a blister that is small, put a felt pad around the blister. You need a donut shaped or U-shaped pad for this to work. You need to put the pressure around the blister and not on the blister. This will stop all of the rubbing that could make the blister get bigger. It will also stop the blister from hurting.

If you running a marathon or competing in an Ironman triathlon and get a huge blister that makes it hard to walk after the race, drain it. You can do this by poking a small hole at the edge of the blister. Heat the needle or soak it in rubbing alcohol. This will sterilize the needle so that you don't introduce any infection causing bacteria when you puncture the blister.

Cover the blister with a bandage that will soak up the fluid as it continues to leak out. If the fluid starts to build up again, then repeat this process and drain the fluid again. Marathon runners with big blisters may have to do this a couple of times. The blister can be quite irritated after running 26.2 miles.

So what are the "exceptions to the rule" about popping or draining blisters in runners?

1. If you notice the blister at mile 13.1 and still have another half-marathon to go, don't pop the blister. This is where the advice from Dr. Oz doesn't fit with runners. If you drain the blister on your heel then continue to run, more fluid will seep under that skin. The skin will slide back and forth. If the drained blister skin slides around, it can't work as a "biologic dressing" because it never has a chance to stick to the underlying raw area. The roof of the blister may also tear. That is what happened in the blister pictured above. All of the rubbing of the heal inside the running shoe caused the blister to rip open. If the roof of the blister tears, it needs to be removed (called "de-roofing" by podiatrists).

If the blister is drained, you need to secure the overlying skin in place with a dressing. Wait until the race is over. If you drain it mid-race it will hurt like hell, there is a higher risk of infection and it will take longer to heal. You also need to wear a pair of shoes that won't rub on the raw blister after it has popped. So once you drain the blister, apply a dressing that will hold the skin securely in place. Change the dressing daily. Studies show that hydrocolloid dressings works best to bake blisters heal fastest. But there is NO evidence than antibiotic ointment helps blisters heal any faster.

2. All blisters should be drained, completely de-roofed and treated by a podiatrist if you are diabetic. The risk of infection is much higher in diabetics. A blister anywhere on the foot in a diabetic runner is a medical emergency. I have personally performed many amputation on diabetics where a blister became hugely infected and spread to the underlying bone. Seek immediate medical attention if you have diabetes and a blister anywhere on the foot, heel or toes.

Although it is easy to prevent blisters, they still often occur in runners. In fact research shows that blisters on the feet are by far the most common running injury reported among marathon finishers. If you get a blister on the feet, treat it right and it will heal quickly so you won't have to miss much training at all.

Dr. Christopher Segler is a sports medicine podiatrist in San Francisco with a focus on runners. He is also a marathon runner and Ironman triathlete himslef. He makes house calls all over the Bay Area to treat running injuries like blisters, stress fractures and Achilles tendonitis. If you have a question about a running injury you can email him or call (415)-308-0833 to reach him directly. For the best source of running injury prevention information in the San Francisco Bay Area, visit or