Are Black Toenails Really A Big Deal For A Runner?

Are Black Toenails really a Big Deal for a Runner?

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Today on the Doc on The Run Podcast, we’re talking about black toenails from running.

Black and Bruised Toenail

Are black toenails really a problem if you’re a runner? Well, that depends. The truth is, NO!…black toenails are not really a problem. They’re just ugly and maybe a little bit painful. But if you are a runner black toenails are pretty common. I mean, let’s face it. Who hasn’t declared their black toenails as some kind of badge of honor when you’re doing your first marathon or you’re finished an ultra marathon?

I see pictures posted all the time from people who are not just first-time marathoners but sometimes world class runners who post pictures of their feet with these really nasty black toenails that are black and blue, bruised, damaged, beaten up, and they post them as “Look at what I survived. I’m tough. I made it through this. I got black toenails and I’m still alive but I finished the race.”

Black Toenails

I understand why people do allow themselves to get black toenails. Let’s face it. Runners are tough. We’re driven. We have goals. We really want to achieve them and we’re not going to let something like an ugly, sore toenail get between us and the finish line. But you have to really think about the real long term risk abuse leading to black toenails.

The first thing is that it is preventable. If you don’t hear anything else, realize that there are some minor things you can do to prevent yourself from getting black toenails when you’re running. So don’t think you have to have black toenails just to be a runner. It’s not the way it is. Either your shoes aren’t fitting correctly or you’re not doing a couple things that can keep that under control, and we’ll talk about that later. But in terms of answering the actual question posed for this episode, “Is it really a problem or not?” There are really two things.

The reason it can be a problem for you is the first thing is that you can get two problems essentially, aside from the pain and all of that sort of stuff that happens initially after you get black toenails. When you get black toenails what has happened is that you’re running and you’re, one of two things is happening. Either you’re running downhill and your toes are hitting the inside of the shoe and they’re getting impacted and it’s pushing on the nail, and that causes basically bruising under the toenail that leads to the dark discoloration that you see as a black toenail.

Sometimes if you do that enough, you can actually get fluid in between the nail plate and the nail bed, and it can lift the nail plate right off the nail bed and then the toenail falls off later. Now that’s a problem in itself, obviously, because it’s painful, you could get a bacterial infection and so on, but as a podiatrist, the thing that I worry about most with patients getting this is one of two particular problems.

Toenail Fungus

The first thing is a toenail fungus infection. When you lift the nail plate up off of the nail bed underneath, if it has an opening, it’s draining and some of the blood seeps out or many people say they can take a paper clip and heat it up and melt a hole through the nail. Well, you’re letting stuff in there. It’s sterile until it pops, but once it pops because you stuck a needle in it, drilled a hole in it, poke a hole in it with a red hot paper clip, all of which, by the way, can put you at risk of lots of different problems. I think it’s a horrible idea to do those things in general, but those are common things I see runners writing about that they have heard as suggestions for way to relief the pressure and get that fluid out. But when you get the fluid out, you can get other stuff in.

Toenail fungus

If you get fungus in there, the fungus will actually grow between the nail plate and the nail bed and that causes a toenail fungus infection. Well, toenail fungus infections are notoriously ugly. I mean, the nails get thick. They get yellow. They get crumbly. They break apart and in some cases they actually smell bad. So, they’re just plain gross. Nobody wants a toenail fungus infection.

Now, it is treatable. I mean, you can treat it with lasers. You can treat it with topical medications. You can treat it with oral pills. There are all different kinds of ways that you can treat it. In many cases, it is treatable but it’s really tenuous. It’s hard to get rid of it. You have to do some stuff and really be careful about not getting re-exposed to it because the nails are so damaged. So even when you kill the fungus, there’s a high rate of re-infection and you don’t want to get toenail fungus in your toenails just because you damaged them, and that starts often with black toenails.

One of my friends, who’s a podiatrist, actually, her son damaged his foot in a soccer game and the nail was loose. She actually wanted to borrow my laser to do toenail fungus treatment sort of preemptively to make sure that he wasn’t getting a fungal infection in that nail because it had been damaged. So she was concerned about that, right, so you might want to be concerned about that too. If you get black toenails and it becomes loose, there’s a real good chance you could get fungus in there and then get a toenail fungus infection. If you’re worried about that, you might want to preemptively try to use some topical anti-fungals or something to prevent the fungus from getting in there and setting in the nail plate, getting in there, setting hold, setting up an infection, to make sure you don’t get these funky, thick, yellow toenails that we see as a toenail fungus infection. Actually, that condition, by the way, toenail fungus, the medical term for is onychomycosis. Mycosis refers to fungus and onycho refers to the nail plate or the toenail plate itself.


The second condition sounds similar. It’s onychodystrophy. Dystrophy just means there’s something wrong with it and it’s misshapen, damaged, whatever. It’s not normal. Onychodystrophy happens with runners who get their nails beaten up time after time after time. If you whack the nails and you beat them up over time, they can become thicker. The reason that happens is the nail plate is actually the same thickness and curvature and everything as the toenail itself.

The nail matrix is basically under the skin at the base of the nail and the nail grows straight out from that root of the nail that we call the nail matrix. When the nail plate is growing out, if you impact the nail because you’re hitting the toe on the inside of the shoe, or your toenail is sort of scraping the inside of the shoe as you’re running uphill and your toes are pulling upward, that as it beats the toenail up, it can sometimes actually impact and squish the matrix and the matrix becomes thicker. When it becomes thicker, the nail’s always going to grow out thicker.

Sometimes I see people who are runners and they’ll say, “I think I have toenail fungus. Can you come look at it? Can you treat it? Can you do laser treatment on this nail and make it prettier, more normal?” And then I look at them and the nail plate is actually, it’s really thick and it’s kind of yellow, but it’s only because it’s really a lot thicker and that thickness is because of this condition called traumatic onychodystrophy.


When you have traumatic onychodystrophy, the nail’s just plain thicker. There’s nothing you could do about it. There’re actually some doctors that try to do microsurgery on the matrix and cut open the nail, skin fold, peel it back, try to thin it out using these little things. We call them loops. It looks like little binoculars on your glasses, but they tried to actually address it and see if they can make the nails grow out normal. It was all a horrible mess because then they got scar tissue. It just made the nails funkier.

So, it’s very difficult to fix. You can’t really make it go away. You can sand down the nails and file them, make them thinner, and they do look better, but they’re still thicker. So when they grow out, you have to do it again and again and again because it’s permanently changed.

Now, that’s different than the toenail fungus. With nail fungus when it gets thicker and you grind it down, it sort of, you get these pockets and little areas where the fungus has eaten away at the nail and it completely looks different. But with traumatic onychodystrophy, sometimes it looks kind of like a nail infection when we first start looking at it, but if we grind down the nail and thin the nail plate down, it actually starts to look a lot better. So it’s easier to make it look good, but it’s a more permanent problem. You can’t just do laser treatment on that and make it look better. You can’t just take oral anti-fungal medications and make the nail look better because you got rid of the fungus because there’s no fungus there.

Those are the two big problems and the two main reasons that podiatrists will tell you, you should not get black toenails. You want to avoid that. The other thing, of course, is that it hurts. If you’re running a race, if you’re doing a 100-mile trail race and you start banging the nails in the shoes. You’re hitting the inside of the shoes and you’re starting to get bruising over the nail and you do that within the first 20 or 30 miles, the last 70 or 80 miles are going to be pretty rough because it’s going to hurt more and more and more. It’s going to get worse because you get fluid accumulated under the nail plate and it gets thicker, which means it’s more prone to getting impacted anyway because it’s taking up more space.

So, the first thing in trying to prevent that, there’re couple of keys. One is obviously make your shoes fit. I know you probably hear this all the time, that all these rules of thumb about what should work and what shouldn’t. But the truth is if you’re running and you’re getting pain in the nails, if they’re sore to the touch after you run, there’s something wrong with the fit of your shoes and you should do something about it, either go bigger, go smaller, whatever. I mean, the fact is if they’re too big, you can actually slide in the shoes and hit the end of the shoe. If they’re too small, obviously, your nails are going to be hitting the shoe all the time.

File the nails 45-degree angle across the edge of the nail

If you have a seam on the inside of the upper in the shoe, then when you pull your toes up, it may catch and sort of hook on the seam or the stitching on the inside of the shoe and cause a similar problem even though you’re not hitting the very end of the shoe inside the toe box. The first thing is check the fit of the shoes. Second thing is to actually cut your nails short. If your nails are sticking way out beyond the end of your toes, obviously you’re going to be hitting them on the end of the shoe more often. They’re going to catch more.

For me, personally, I know that I can go and do a marathon without any problems as long as I file the nails down. I actually file them at a 45-degree angle across the edge of the nail. That way they’re not prone to hitting the inside of the shoe on the upper when I run uphill. Also, the second thing you can do is aside from making sure they’re not just sort of more abrasive and that edge isn’t really going to catch on anything is to put a skin lubricant like Body Glide or something like that on the surface of the nail. So, if you have, like your second toes, for example, if you know they always get bruised, they always get damaged, you should just try that.

Before your next race, before your next long run, just put some skin lubricant on the surface of the nail and see because if it’s friction where it’s catching the inside of the shoe very, very slightly, then if you put skin lubricant on there, it will decrease that friction enough that it won’t be a problem. Now, if you have the same amount of bruising after you’ve done that, then it’s probably more an issue where either the nails are too long or the shoes are too short and you’re impacting the inside of the shoe, or it’s running downhill and your shoelaces are too loose. But you have to figure out what the problem is, why you’re getting black nails, why you keep bruising your toes because it can be a problem.

Also one thing that’s not talked about a whole lot but it is really common is that the skin folds on the side of the nail, they’re basically grooves that are held in place by the nail plate itself, which is sitting there kind of acting like a strut between those nail folds. If you run and you get a big bruise under the nail and a big collection of fluid that lifts the nail plate off the nail bed and then you loose it, it takes months and months for that nail to grow back out. While you’re waiting for that nail plate to grow back out, the skin at the end of the toe can kind of contract and then makes it a tighter fit for the nail as the nail grows in. That then can make you chronically prone to ingrown toenails, which can also be this recurring painful problem.

Cut the nails short

There are many reasons that you have to worry about black toenails, and truthfully, yes, it’s kind of cool if you can say, “Hey, look, I survived. My toes are all black and blue.” People put those kind of pictures online all the time to sort of show that they made it through a race. They survived, they toughed it out. They still finished, they got their medal, but you want to avoid that and it is mostly avoidable. You do not have to wind up with black toenails. It’s not a thing that you have to get because you just ran a race. It’s a thing you get because you have some issue that you could address and make sure that you don’t wind up with black toenails.

So pay attention to these things. Try filing the nails. Try some skin lubricant. Try to change the shoes that you’re using, and then see if you can’t make it through your next long run or your next race without these problems. That’ll help you avoid the other things like toenail fungus, like permanently thickened toenails, and potentially even chronic ingrown toenails from something that is completely preventable. And all of that is going to help you, of course, keep running, keep active, and stay out there on the course a lot longer with a lot less problems.

If you have a question that you would like answered as a future addition of the Doc On The Run Podcast, send it to me And then make sure you join me for the next edition of the Doc On The Run Podcast!

Dr. Christopher Segler is a podiatrist and ankle surgeon who has won an award for his research on diagnosing subtle fractures involving the ankle that are often initially thought to be only ankle sprains. He believes that it is important to see the very best ankle sprain doctor in San Francisco that you can find. Fortunately, San Francisco has many of the best ankle sprain specialists in the United States practicing right here in the Bay Area. He offers house calls for those with ankle injuries who have a tough time getting to a podiatry office. You can reach him directly at (415) 308-0833.

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