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Black Toenails From Running: Causes, Prevention And Treatment

Black toenails are one of the most common problems experienced by runners, particularly those training for half marathons, marathons and ultramarathons. While they can look alarming, they are usually more of a nuisance than a serious injury. Many experienced runners have lost one or more toenails over the years, but that doesn't mean it's something you should simply accept as inevitable.

Black toenails are one of the most common problems experienced by runners, particularly those training for half marathons, marathons and ultramarathons. While they can look alarming, they are usually more of a nuisance than a serious injury. Many experienced runners have lost one or more toenails over the years, but that doesn't mean it's something you should simply accept as inevitable. Alongside blisters and sore feet, black toenails are often a sign that something about your footwear or foot care needs attention. Understanding why they develop and taking a few simple preventative steps can help you avoid unnecessary discomfort and keep your training on track. What Causes Black Toenails? Black toenails are almost always caused by repeated trauma rather than one specific injury. As you run, your toes can repeatedly strike the front or top of your running shoes. Over thousands of strides this repeated impact damages the tiny blood vessels beneath the nail, allowing blood to collect underneath and causing the nail to turn dark purple or black. Long-distance races make the problem more likely because your feet naturally swell as the miles pass. This reduces the available space inside your shoes and increases the amount of pressure placed on your toes. Running downhill can also make matters worse because your feet slide forwards inside the shoe, increasing the force applied to the front of the foot with every step. Which Toenails Are Most Affected? The big toenail is the one most commonly affected because it usually experiences the greatest amount of pressure inside the shoe. However, the second toenail is also frequently damaged, particularly if it is naturally longer than the big toe, which is perfectly normal for many people. If you repeatedly develop a black toenail on the same toe, it is usually a sign that your shoes do not fit quite as well as they should or that your foot is moving excessively inside the shoe while you run. Can The Nail Fall Off? Although it can be unsettling the first time it happens, it is usually nothing to worry about. If enough damage has occurred beneath the nail, it may gradually loosen over several weeks before eventually falling off on its own. In most cases a new nail will already be growing underneath, although it can take many months, and sometimes up to a year, before it looks completely normal again. During this time it is important to keep the toe clean and protected to reduce the risk of infection while the new nail develops. Should You Keep Running? Whether you should continue running depends on how painful the toe is. If the discomfort is mild and the nail is simply discoloured, many runners are able to continue training without making the injury any worse. However, if the toe is extremely painful, swollen or throbbing, continuing to run is unlikely to be comfortable and may increase the risk of complications. Occasionally, a large collection of blood beneath the nail creates enough pressure to require medical treatment to drain it and relieve the pain. As with any injury, avoid changing your running style to compensate for the discomfort. Altering the way you run to protect one sore toe can place unnecessary strain on your feet, ankles, knees and hips. How Can You Prevent Black Toenails? The most effective way to prevent black toenails is to wear running shoes that fit properly. There should be enough room in the toe box for your toes to move naturally without repeatedly striking the front of the shoe. It's also important to remember that your feet swell during longer runs, so shoes that feel comfortable over shorter distances may become much tighter during a marathon. Keeping your toenails neatly trimmed is another simple but effective preventative measure. Long toenails are much more likely to catch on the inside of your shoe or your socks, increasing the repeated trauma that eventually causes the nail to bruise. Your lacing technique can also make a significant difference. Many runners benefit from using a heel-lock or runner's loop lacing method, which helps hold the heel securely in place and reduces the amount the foot slides forwards inside the shoe. Technical running socks can further reduce the risk by minimising friction and helping to keep your feet dry throughout longer runs. If you're buying new running shoes, having them professionally fitted is well worth the time, particularly if you're training for longer distances. Read more about running socks here. Getting your lacing right is more important than you think Looking After Your Runner's Feet Black toenails are only one of several foot problems that affect runners. Looking after your feet should become part of your regular training routine rather than something you only think about once an injury develops. Inspect your feet regularly after longer runs, paying attention to any hot spots, blisters or areas of rubbing before they become more serious. Keeping your feet clean, allowing your shoes to dry properly between runs and replacing worn-out footwear will all help reduce the likelihood of foot problems developing. If you regularly develop hard skin or calluses, avoid removing them completely. A moderate amount of callus provides natural protection against friction, while removing too much can actually make your feet more vulnerable to painful blisters. Read more about blister prevention here. When Should You Seek Medical Advice? Most black toenails recover perfectly well without any medical treatment. However, you should seek professional advice if the pain becomes severe, the toe becomes increasingly swollen or you notice signs of infection such as redness, warmth, pus or increasing tenderness. It is also important to have any dark mark beneath a toenail checked if it appears without any obvious injury or running-related cause. Although this is uncommon, not every black toenail is caused by running, and it is always sensible to rule out more serious conditions. Final Thoughts On Black Toenails From Running Black toenails are an extremely common consequence of distance running, but they are rarely something to worry about. In most cases they simply indicate that your toes have been subjected to repeated pressure over many miles rather than any serious injury. By choosing well-fitting running shoes, keeping your toenails trimmed, using appropriate socks and paying attention to the first signs of rubbing, you can greatly reduce your chances of developing black toenails in the future. Looking after your feet may not be the most exciting part of marathon training, but healthy feet provide the foundation for every successful run and will help keep you comfortably moving towards your next finish line.

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