How to Avoid Blisters and Black Toenails from Running - DOC

How to Avoid Blisters and Black Toenails from Running

San Francisco Podiatrist and Marathon Runner Explains

San Francisco, CA – March 31, 2010 

The vague stinging and burning sensation emanating from a blister can easily detract from your focus during a marathon. The more you think about it, the worse it gets.  The next thing you know, your pace is off, you speed up and slow down because of this unpleasant distraction. When you walk through a water station, it just gets worse, and you start to limp. After the race, running is out of the question. You may even limp for days while back at work.  This is almost always preventable. 

Skin injuries are very common among marathon participants. In fact, a 12-year study of injuries at the Twin Cities Marathon found skin problems (blisters, black toenails, abrasions) to be more common than musculoskeletal complaints (sprains, stiffness, stress related injuries). A whopping 91% of all skin injuries were blisters.  In the most comprehensive study ever reported regarding injury among marathon runners, 7-27% of runners who sought treatment after a race were being treated for blisters.  But don’t be confused…common does not mean unpreventable.  


So what exactly is a blister anyway? A blister (in the case of a runner) is an accumulation of plasma under a pocket of otherwise intact skin that results from repeated mechanical irritation: friction. The repeated rubbing of a sock or shoe against the skin actually causes the top layer of the skin (epidermis) to separate from the layer below (dermis). Fluid seeps from the injured tissue and fills the space, creating the soft fluid filled sack that hurts whenever you step on, push against or otherwise antagonize it.

In mountaineering, there is a saying that frostbite can only result from inadequate equipment or poor planning. No one heads up to the summit of Mount Everest to test out a fancy new pair of mittens. And no one should head out on a marathon course to test out a pair of socks they bought at the expo after packet pickup. 

The easiest way to avoid blisters is consistency of equipment, pace, and conditions. Let’s talk equipment. In general, cotton is one of the worst materials for endurance athletes—so don’t use it. Socks made of synthetic fibers that wick moisture away from your skin help decrease moisture that can make the skin more vulnerable to friction. There are also specialty socks that have dual layers to decrease the friction against your skin. If you seem to be prone to blisters, you can (and should) experiment with some of the many high-performance socks that are available. Experiment in training, but never on race day. 

Your shoes must be broken in as described in the article on shoes. They should be dry when you start the race. Shoes should fit snug (no heel sliding around). I usually alternate my shoes so that I don’t run in the same pair two days in a row.  This allows time for them to dry out completely before I run again. If it is raining, not much you can do. If it is hot, try not to soak your feet when you pour water over your head. 

If you seem to always get blisters on long runs, something is wrong. You may not have the right size shoes or you may not be lacing them correctly. The location of the blisters can often speak to the cause of the problem.  For example, if you walk 50 feet and run 50 feet for the marathon, all of that stopping and starting will cause blisters on the ball of the foot. Try to keep an even pace. Although your running style and gait pattern can contribute to blisters, this is rare. Ask for help and seek the advice of an experienced runner, specialty shoe store or podiatrist. Many people swear by moleskin, body glide, or Vaseline. All can help, for different reasons, but these can also cause the skin to retain more moisture to varying degrees. 

Black Toenails 

Black toenails are almost always caused by tight shoes. If your shoes are fitted correctly but you run down hills (a lot) then your toenails can repeatedly bump the end of the shoe. Whether you hit it once with a hammer or thousands of times on the inside of a shoe, the cumulative trauma can still cause bleeding and bruising of the toenails. The nail plate may be sore and just pinkish right after the race, but often turn dark purple or black after only a day or two. If it is very tender, the blood can often be drained to relieve the pressure.

Preventing Problems on Race Day 

As race day approaches you should be fine tuning your plan and equipment. No major overhauls. If you try new shoes or socks, do it on a short run.  If that goes well, try a slightly longer run. Keep in mind an episode with a bad blister now could stall your training and derail your event. Proceed with caution and good common sense.  Shop the expo and have fun. Treat yourself to some fancy new gear, high performance socks and whatever else your heart desires. You will have earned it after all that training.  Just don’t use any of it until your first recovery run after the big day. Use the tried and true, and you will walk tall and proud after you cross the finish, instead of hobbling to the medical tent.

Dr. Christopher Segler is nationally recognized Podiatrist in San Francisco. He is also a multiple Ironman finisher and marathon runner. His podiatry practice focuses on athletes in training. Because he competes in Ironman events, he understands the importance of getting professional help without missing work or a workout. To help runners stay on track, he offers podiatry sports medicine house calls in the SF Bay Area. You can reach him at 415-308-0833