Runners Toe: What Causes Black Toenails in Runners

Runners Toe: What Causes Black Toenails in Runners

Unless you’re brand new to the sport of running, you’ll have experienced black toenails, more commonly known as runner's toe. It's one of those running injuries that is almost seen as a right of passage amongst runners. You're not considered a 'real runner' until you've lost a toenail or two.

So you may be wondering why exactly do your toenails turn black, what causes it and how do you prevent or treat your black toenails? Let’s find out…

Physiologically, black toenails are caused by bruising or bleeding under the nail caused by bleeding under your skin (subungual hematoma) and the condition can range from mild to severe. This bruising or bleeding beneath the nail is what causes the nail to turn black.

What is causing your toenails to turn black when you run


For runners, the main cause of black nails is the repetitive trauma on your toes from ill-fitting shoes. As you run, the motion of your foot in your shoe causes your toenails to hit the front of your shoes as well as the top of your toe box, thereby damaging the blood vessels under your toenails and resulting in the bruising and blackening of your toenails.

In extreme cases of runners toe, this constant jarring against the front of your shoe (It's like you when you stub your toe, except you're doing it over and over) can cause your nail plate to lift away from your nail bed.

When you run your feet swell, and then get compressed by your shoes and socks. This puts pressure on your feet and damages your toenail beds as the extra fluid in your feet causes the toenail to separate from its bed and subsequent bleeding turns your toenail black.

Wearing the wrong socks, frequent downhill running and long-distance running can also cause black toenails.

How to keep your toenails when they turn black
Pro Tip: If you're worried about losing your toenails then listen to this episode of the Coach Parry Podcast for some tips in how to prevent losing yout toenails when they turn black.

Can't Listen now? Read the full transcript
Welcome back, you’re listening to the Ask Coach Parry podcast, I’m Brad Brown, Lindsey Parry with us once again. Lindsey, a question in from Joan Viljoen. I’m laughing because it’s almost a bit of a badge of honour amongst ultra runners. Joan says, my second toe’s nail on both feet keeps getting upset and eventually falling off, is there anything she can do to prevent black toenails and her toenails falling off?

Lindsey Parry: Look, there’s a couple of things and unfortunately none of them are guaranteed to bring success. Effectively, particularly if it’s happening on the second toe all the time, then you’re just like me, your second toe is actually either the same length or slightly longer than the big toe. Which means that any and every shoe is made to curve from its longest point, which is your big toe and down.

It means, unfortunately that that toenail is always going to be in the firing line. The most obvious thing is to keep toenails really short, so before you do any long run, make sure that those toenails are short.

I’ve got another toenail that cuts its neighbour and it happens all the time. I only know that I need to cut my toenails when my toes maim each other and my toes are bleeding. Unfortunately that’s human nature.

Why a good pedicure could prevent your toenails from going black and falling off

If you are anal about it and you make a note somewhere in the house that you know that every time you’re running a long training run or a race you make sure you cut your toenails as short. They can go without actually hurting the nail bed, that will help a lot.

Filing it down so it’s smooth and there are no rough edges that can catch on the sock or the shoe, that’ll help too. Obviously being in the right size shoes will make a big difference. So when you are at the shops, make sure that you’ve got the right size shoe.

How to know your running shoes are the right size

The simple test is to put them on, tie the laces and if you can fit your thumb between your heel and the back of the shoe without like really being uncomfortable in there. It should be tight, but fairly easy to get in and out and if you can put your thumb on your nail and you can feel about a thumb’s distance between your toe and the shoe, then you know that you’re in the right size shoe.

You can also cut your actual shoe. Right where that big toe is, if you just cut a little half-moon so that the material flaps up, then if it is the toe catching on the top of the shoe, it’s normally the toe catching on the sock or the top of a shoe.

If you release that pressure, then often it takes away that chaffing and it can save the toenail. Try those things. Either way they’ll make a difference, whether it completely saves a black toe or not, time will tell. But it will make it a little less painful and uncomfortable for sure.

BB: There we go Joan, thank you very much and ja, best of luck. But like I say, sometimes it is a bit of a badge of honour getting those black toenails. They’re not pretty but ja, it’s one of those things, I guess, it comes with the territory. Lindsey Parry, thank you very much for your time.

Runners Toe: How to treat black toenails


For mild cases, no treatment is necessary for your black toenail as it will grow out over time. However, subungual hematomas can be painful and the more blood there is between the nail and your skin, the more it will hurt.

If you find it painful you should seek medical treatment and go see your doctor who may recommend trephination.

Trephination is a medical procedure where a small hole is poked through your nail to relieve pressure and help save the nail itself. This procedure should be done by a licensed doctor and should not be performed at home by yourself.

Removing the nail is also not advisable as this may lead to infection.

With the repetitive trauma of frequent running, the toenail may start the process of falling off due to the damaged tissue of the nail bed.


What to do if your toenail falls or rips off


Often the nail will just fall off without much pain or bleeding, but if your nail rips off and opens a wound then you should apply pressure until your blood clots and the bleeding stops.

After the bleeding has stopped, apply an antibiotic ointment and bandage your toe up to prevent infection. Apply the ointment every day until the wound has closed and started the healing process.

Take care as infections can be dangerous. If you experience more pain, swelling and redness, it may be a sign of infection and you should see your doctor. Infections can lead to gangrene or blood infections.

As a precaution, you should also apply some antibiotic ointment even if your toenail falls off without any bleeding. A new nail should grow within 8 weeks.

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How to prevent your toenails from turning black


The most common cause of black toenails is ill-fitting shoes so the best way to prevent your toenails from turning black is to make sure you get the right running shoes.

Try getting a pair that is half a size to one size up from your usual shoe size to make sure there’s a little bit of space between your longest toe and the end of the shoe.

This will help ensure your toes aren’t hitting the shoes as you run. So making 100% sure your shoes fit is the first step to preventing yourself from getting runners toe.

Another way to prevent your toenails from turning black is to keep them short! Make sure you regularly clip your toenails so that they aren’t jutting out and hitting your shoes or cutting into the surrounding skin of your toes.

Wearing the right socks will also help prevent black toenails as a good pair of running socks will help prevent your foot from slipping. You need to wear thin, moisture-wicking socks and avoid thick socks made from materials like wool or cotton.

If you use some form of lubricant on your feet or toes to prevent blistering, it's important to not use too much. Lathering your feet in something like vaseline or body glide could prevent blisters but cause your feet to slide around excessively.


Other causes of black toenails


Fungal infections are another cause of discoloured toenails and can turn your toenails various shades of yellow, purple, green, blue, brown and black. The toenail fungus also results in subungual debris (a chalky, white substance) around your nail bed. If you think you may have a fungal infection, go and ask your doctor. They are able to do a biopsy and recommend treatment options.

In rare cases, a black toenail can also be caused by a subungual melanoma, which is a type of skin cancer that affects the nails.

While black toenails that are a result of trauma, like from running a marathon, appear quite suddenly, a subungual melanoma will appear as a black line beginning at your cuticle and extending up into your nail. If you are concerned about your black toenail, you should consult your doctor for medical advice.

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