A surprisingly common running injury is the infamous ‘runner’s toe’ (also known as runner’s toenail), which can leave us runners with bruised toenails from running, black toenails, and even toenails falling off, as well as simply just having sore and aching toes and nail beds.
Runners toe occurs when there is repeated trauma to the toenail or nail bed. This repeated impact can cause bleeding underneath the toenail, which in turn makes your toenail feel bruised, turn black or otherwise get discolored, or even fall off.
In addition to causing toenail issues, the repeated impact on the toe end of your feet can also be the reason for other toe pain, including a blood blister under your toenail and aches caused by the associated stress to your toe tissues and joints.
I know, having your toenail turn black, purple, or even fall off completely is unpleasant to deal with and even talk about, but the good news is that if you understand what causes this condition, then it’s highly preventable.
Trust me – as an ultramarathon runner who’s completed many long training runs and races over punishing, rocky and technical trails I know a thing or two about how to avoid running injuries such as this, and I’m here to help!
In this post I explain the symptoms, what causes it, and the simple things you can do to prevent and treat runner’s toe.
What causes runners toe (aka a subungual hematoma)?
Several factors can contribute to cases of runner’s toe. The most common causes among running communities include repetitive impact and tight-fitting shoes – or shoes that aren’t the right size for your feet.
Essentially, what’s happening inside your shoe is that the end or top of your toe repeatedly hits or presses up against the inside of your shoe.
Symptoms of runner’s toe
The repeated impact of your toes hitting your shoe when running or hiking can cause blood vessels in the toe to burst, resulting in bruising and discoloration from bleeding under your nail.
In more extreme cases, the toenail may become detached, meaning some runners have their toe nails come loose or fall off completely.
In other cases, you may experience a painful blister underneath your toenail and the toenail may start to come away from the toe, which is why you may have heard some runners complain about their toenails falling off.
What’s the cause of black toenails?
If you’re wondering why you have developed a black toenail from running, the black color you see is essentially from bruising, which is underneath your nail and can make the nail look black.
A medical professional may refer to the bleeding under a nail as a subungual hematoma, in case you’d heard that term and were wondering what the heck one of those was!
You can get a similar injury from a one-off impact to your toenails (or fingernails), such as stubbing your toe on a hard object or catching your finger in a car or house door.
It can affect any toe, although runners most commonly complain about getting a sore or black toenail in their longest toes, so either the big toe or second toe.
Does long-distance running cause your toenails to turn black?
While you may hear or read that running long distances can increase the risk of developing this issue on the basis that the feet are subjected to prolonged impact and pressure when you run for longer periods of time, as an ultra runner myself I would disagree with that.
If your shoes and socks are correctly fitting, and your toenails are adequately trimmed and maintained, then running long distances should not really increase your risk of damaging your toenails.
Nor, for that matter, does doing a lot of downhill running (often cited as a ’cause’ of this injury).
It may also be useful to know that while having purple, black and blue toenails is a common injury among runners, it can also affect anyone who engages in high-impact activities, such as hiking or playing sports.
By understanding the causes, you can take preventative measures to protect your feet and nails from this painful and uncomfortable condition.
Ways to prevent runner’s toenail (black toenails from running)
Here are the 4 most effective ways to prevent black toenails from running.
1. Wear running shoes that fit your feet correctly
As mentioned above, a common cause of black toenails and associated pain is from wearing shoes that do not fit you properly. Getting properly fitting shoes is the single best way to prevent this issue.
Often the cause may be because your running shoes are too small, too tight or narrow in the toe box area and your toes are pushing on the end of your shoe.
However, black toenails can be signs that your shoes are actually too large or simply not done up tight enough.
If your laces are not holding your foot securely in the shoe then your foot may slide forward inside the shoe and push on the end each time it hits the ground.
This can be particularly problematic if you’re a trail runner or running up and down a lot of hills, where gravity and impact will be more likely to force your foot forward towards the end of the shoe.
Your shoes should fit correctly and be laced up well to prevent the foot from sliding inside the shoe, which can not only cause bruised toenails but is also a recipe for getting blisters on your feet when you run. They should also provide enough room in the toe box for your toes to move freely.
For guidance on choosing the right footwear, visit our buyer’s guides to road running shoes, trail running shoes and hiking boots for tips and our recommendations.
2. Proper nail care
Trim your nails regularly. This is the second most important way to ensure you don’t get a black toenail from running.
When you trim your nails, it’s best to make sure to cut them straight across rather than rounded, although I like to round off the sharp corners to prevent any rubbing of nails on the adjacent toes. It also stops the nails from catching on socks and causing holes and other issues.
Use a sharp toenail clipper, not nail scissors, for a clean cut.
It’s often the case that if you already have properly fitting running shoes, a simple nail trim can stop your nails from pushing on the end of your shoe and causing discomfort.
On longer runs they may even push on socks, which can cause pain after a long time running, so keeping them trimmed reduces the possibility of this happening.
Keeping your nails clean and dry can also help prevent infections that can contribute to other toe and foot issues.
3. Proper running technique
Good running technique is critical in preventing running injuries, including runner’s toenail.
If you find that you tend to shuffle your feet or land heavily when you run, then this could be contributing to your toenail issues.
Our popular guide to running with proper form is a must-read if, like many runners, you feel you could benefit from improving your running efficiency and style.
4. Wear well-fitting running socks
A good pair of running socks should fit you well, so they’re not too loose (which can allow your feet to slide around inside them), but not too tight – which can be a cause of runner’s toenail.
Yes, socks that are too small may press on your toenails over thousands of steps when you run, and that can bruise your toe or cause pain in the nailbed from the pressure – especially if you haven’t adequately trimmed your toe nails.
This can also happen if you wear overly thick socks that can put pressure on the top of your toe when it’s squished in to a shoe with a relatively small toe box.
So, make sure you are wearing well-fitting socks designed for running in. Proper running socks will not only help with preventing runner’s toe, but they should also help keep your feet comfortable and dry because of their technical, sweat-wicking fabric construction which can help prevent issues such as athlete’s foot, a common fungal infection.
If you need some new socks, visit our best running socks buyer’s guide for guidance on the best running sock brands.
Treatment for Runner’s Toe
Most people with this injury have nothing more than a bit of bruising and the inconvenience of getting a black toenail, which can look unattractive!
If that sounds like you, then there’s not much to treat as it’s best to let your body heal itself and take the preventative measures set out above to ensure the problem doesn’t get worse, or happen again.
Let black nails grow out
Black toenails will eventually grow out.
If you don’t like the look of them then get creative! You can always paint your nails to disguise the color – or just show them off as running battle-wounds. I mean, who really cares? You’re a distance runner and that’s badass, black toenails and all!
See a podatrist or doctor
Some people are unfortunate enough to experience more significant pain in their toenails or general toe area.
This may be the case for you if you have more severely damaged your toe underneath the nail, and have an issue such as a large and painful blister underneath your toenail that’s causing pressure.
Other people who have damaged the nail bed more severely may find it’s caused their toenail to separate from the toe.
Plus, there’s always the possibility that your toe pain is caused by something else, rather than runners toe-related bruising.
If you’re concerned, see a professional such as a podiatrist or your doctor who can inspect and treat your toe, as well as any potential infection.
You definitely want to get some help if there’s pain for more than a couple of days as it may be necessary to take medication such as antibiotics to treat infection, which could be a serious complication.
Potential treatments they may offer you include removing damaged nails, or bandaging the toes to help you hang on to the nail as long as possible until a new one grows through in its place. Because the nail is there to protect your toe it’s often best to keep it on there, if you can!
Another treatment that may be offered is a procedure called nail trephination. This is a fancy way of saying they’ll drain the blood and other liquid that may have accumulated under the nail, which can help relieve pressure and pain.
You definitely want an expert to do this because there is a risk of infection and it needs to be done properly. It is typically done in a doctor’s office and can provide quick relief from pain and swelling.
The nail trephination procedure involves creating a small hole in the nail with a heated needle or a specialized tool, allowing the blood to drain out. The procedure is simple and generally safe, but there is a small risk of infection or damage to the nail.
While runner’s toe is a common condition among athletes, particularly runners, that can cause pain, discomfort, and cosmetic issues like black toenails, it can be easily prevented with proper footwear, paying attention to running form and keeping your toenails trimmed appropriately.
If it does occur, mild cases can often be managed at home and more severe cases may require medical intervention such as nail trephination or antibiotics.
With prompt treatment and care, it can usually be easily resolved, so you can get back to your marathon training and wearing open-toed sandals!
If you are planning to run a marathon in the coming months, head over to our training plans page to download a free training plan for your race goal. Also check out our Running 101 page for loads more running tips and advice to help you run stronger, faster and injury-free!