Is this black toenail fungus or a bruised toenail from running?

I have been training for a trail run and have been running on lots of hills in Marin. I recently noticed that I was getting some dark black discoloration of my toenail. I am worried that this might be black toenail fungus infecting the toenail. How can I tell whether the toe is bruised or if I really have a toenail fungus infection? Also, what if anything should I do to treat the black toenail if it is infected?

Thanks,
David, Mill Valley, CA


Black toenails are likely one of the most common injuries I see in runners in Houston and San Francisco. There can be a couple of causes of black toenails from running.

Differences between a bruised toenail and a fungal toenail:
A bruised toenail hurts because 1) there is bruise 2) there is blood under the toenail increasing pressure between the toenail and underlying nail bed. This causes pain in the toenail when you press on it or bump the toenail on the inside of your shoes. Fungal toenails are not usually tender unless the toenail infection has been present long enough to make the fungal nail really thick.  The increased thickness can cause some tenderness, but it doesn't happen quickly.

A bruise comes on quickly, but a toenail fungus infection appears gradually. Bruising will appear within a day or two of your long run, race or whatever injury to the toenail. If you kick a coffee table once with your toe, the toenail may develop a bruise and turn black. If you bump the toe inside your running shoe repeatedly while running down hill (or because the running shoes are too tight) you can also get a bruised black toenail from the cumulative trauma. This can happen overnight.  You wake up and the toenail is black.

The changes in the toenail caused by toenail fungus happen very slowly. The color of the toenail will not change quickly.  The increased thickness, yellow discoloration, white crumbly appearance and dark color of a fungal toenail infection happens so slowly that it is almost hard to notice.

You can learn more about black toenails and toenail fungus treatment here by reading about an example of a black toenail in Houston that actually is just a toenail bruise. You can also read about from runners, blisters and black toenails here.  Learn how a bruised toenail can lead to a toenail fungus infection.

Dr. Christopher Segler, Doctor of Podiatric Medicine is Board Certified, American Board of Podiatric Medicine. He is a 10-time Ironman finisher and marathon runner. He lectures frequently to other podiatrist and foot specialists at medical conferences on the treatment of complicated running injuries and running biomechanics. He is licensed to practice podiatry in Texas, California, and Hawaii. He travels back and forth between Houston and San Francisco to see injured runners who have running injuries that need the fastest treatment based on a runner's goals and running doc perspective. If you live in San Francisco or Marin and have a running injury question call 415-308-0833 to speak to him. If you are in Houston and have a question about a running injury, call him directly at 713-489-7674. 

San Francisco Podiatrist Explains Why Athlete's Foot is Common in Bay Area Runners and Cyclists

Athlete's foot is a fungus infection of the skin that often occurs in runners, cyclists and other athletes. It just so happens that the San Francisco Bay Area has a climate that can make it easier for you do develop a case of itching, burning, peeling feet that characterizes the condition.

In order for any fungus to grow best, it needs a habitat that is dark, warm and moist. As it turns out, shoes are perfect for this. You put on your running shoes and head out for a run through Golden Gate Park. Your feet sweat (even if it is fifty degrees), and the heat from your feet turns the shoe into a little incubator for the nasty stuff to grow. If it is like many days in San Francisco, you may even get some rain or light drizzle further soaking your shoes. Then you get home and toss your shoes in the closet until you get ready to go for a run the next day.

The problem is that very few closets have heat or air conditioning vents in them. For this reason, the shoes just won't dry out. They stay damp. And damp running shoes equals fungus.

Cyclists have a similar problem. Head out on the road to Nicassio or anywhere else in Marin county on the weekend and you will see hundreds of cyclist out for a ride. Most of them are wearing shoe covers to help keep their feet warm and dry. But these shoe covers don't breathe very well. As a result, all of that moisture gets trapped inside the cycling shoes. Once the ride is over, many cyclists will toss there shoes in the garage right next to their bike. Sitting in a cool and damp garage keeps the inside of those cycling shoes damp as well.

Sooner or later, the fungal spores in the shoes will cause an athlete's foot infection. Often this is just nothing more than mild peeling of the skin on the bottoms of the feet (see picture above). But some people get severe itching, redness and burning of the feet. Once in a while a secondary infection (caused by bacteria) can start an even bigger problem.

So what to do?

First off, it is very easy to prevent athlete's foot by simply drying your running shoes and cycling shoes out. Bring them inside. I usually leave mine near of a heating vent for a couple of hours after I go running or biking. This ensures that the insides of the shoes will stay dry. Dry shoes don't support fungus very well. If you wear cycling shoe covers, take them off after every bike ride to help them dry out.

If you do get athlete's foot, over-the-counter (OTC) anti-fungal treatment creams will usually cure the problem in about 4 weeks. All you have to do is follow the directions on the tube. Make sure you use the cream for about a week after the problem seems to have gone away. Otherwise you might still have some fungus in the skin that can flare back up in only a couple of weeks after you stop applying the anti-fungal medicine.

Keep in mind that if you get athlete's foot, you will have been shedding fungal spores in your shoes. You need to decontaminate them by spraying lysol in your shoes and letting them dry out thoroughly afterward. If the athlete's foot doesn't improve after you treat it yourself with OTC medications, see the best podiatrist you can find.

Dr. Christopher Segler is a runner and Ironman triathlete who practices Podiatry in San Francisco. He offers house calls to busy athlete's through www.DocOnTheRun.com. You can learn more about common causes of foot pain at www. AnkleCenter.com, San Francisco's best podiatry treatment information site.