Having your toenails turn black is a potentially serious problem that can happen to anyone, but is particularly common among long distance runners.

The first thing many runners think when a toenail becomes black after a run is that their shoes are too small and their toes are hitting the end of the shoe. However, improper shoe size is usually not the cause.

Your shoes may NOT be the cause of your black toenail.

Instead, what happens is that the pressure on the ends of the toes increases as you run longer distances and become more fatigued. This is because the muscles and tendon that flex your toes become more active as the other muscles begin to tire. As a result the toes begin to “grip” against the bottom of your shoe. Once the toes start gripping a significant amount of pressure is created at the tips of the toes. Your longest toe and/or the one that grips the most are the toes most likely to be affected. The pressure on these toes increases to the point that the nail area gets “bruised” from the repetitive trauma of every step. Eventually blood starts to accumulate under the nail resulting in a black toenail.

The pressure of blood accumulating under the nail can cause significant pain.

However, if you’re lucky the pressure that causes your nail to turn black will happen gradually enough, that it won’t be painful and you won’t lose the nail. You may not even notice that your toenail turned black. In these cases, the blood under the nail dries out as fast as it forms. You will simply have to wait for the nail to grow out or for “blackness” to clear from the nail.

If, however, the blood accumulates too quickly and/or you keep on traumatizing the area (i.e. running a marathon) then the nail will lift and it may feel like you have a blister under the nail. Besides being extremely painful this creates a high risk of infection because there is a high concentration of bacteria under the toenails. In this case you should definitely seek medical treatment. You may have to have the fluid drained and possibly even have the nail removed.

Usually, after the initial symptoms of a black toenail resolve, a new nail will eventually re-grow. However, it can take from eight months to more than a year for things to return completely to normal, and if you keep running during this time …. The nail area should be closely monitored as the new nail is growing. In some cases the lifted area of the old nail can become embedded in skin as the new nail is trying to push it out. This may result in pain, ingrown toenails, and even secondary infection. In addition it is very common to develop a fungal infection at the site of a previously damaged nail. After the bleeding lifts the nail from the nail bed fungus can infiltrate the space between the nail and the skin. The area provides the perfect dark, moist environment in which the fungus thrives.

Black toenails may seem like a minor problem at first, but, besides the risk of infection, they can create problems that develop long after the initial injury.

If your long runs are causing your toenails to turn black remember to observe closely even if they’re not painful. And if there’s any pain, swelling or redness you should call your podiatrist immediately. An infection in the nail area will certainly result in time missed from training!

If your suffering from a toenail injury or have questions about your foot or ankle call 562-433-0478.

Richard H. Graves, DPM
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Podiatrist, Sports Medicine Specialist