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 runner 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.

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.

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 into 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 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.


With a passion for high performance sport – Lindsey Parry is one of South Africa’s most widely recognised coaches. Having led a team to the London, Rio and Tokyo Olympic Games as well as the Commonwealth Games in Edinburgh, the Gold Coast & Birmingham, and coached both triathletes and runners onto podiums of some of the world’s most illustrious races, Lindsey has a unique ability to understand what it takes to succeed at any level and thrives on coaching, motivating and inspiring others to do the same – whether it’s on the track, on stage or behind a mic.

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