Buzz
Black toenails are a common issue for marathon runners and other dedicated athletes, but it's something you can avoid. Often, the problem lies in how your shoes fit, so here’s a guide on how to prevent black toenails from occurring and how to address them if they do.
And yes, in case you were curious—sometimes a black toenail might fall off. If you've never experienced this, you’re probably grossed out right now. But if you have—and I’ve been there—you’ll find it’s not as big of a deal as it sounds, and it eventually grows back. More on that later.
What causes toenails to turn black?
A black (or blue or purple) toenail is typically just a bruise that's visible because your toenail is transparent. That’s what we’ll focus on here. These bruises can appear suddenly, like if a weight plate falls on your toe, or they may develop gradually from repeatedly bumping your toes against the front of your shoes as you run.
There are other reasons your toenail may change color, so if you’re unsure whether it’s just a bruise or something more serious, it’s best to consult a healthcare professional. Other causes include normal color changes over time, various types of toenail fungus, or even skin cancer. If the color change spreads beyond the nail, or if a black spot remains for months instead of fading, it could be cause for concern. But in most cases, if your mileage has increased and your toenails start to turn black, the reason is likely straightforward.
Go for a larger shoe size
Bruised toenails are common among frequent runners, but they aren’t guaranteed. If you find your toenails constantly bruising, it’s likely that your shoes are too snug in the toe area.
I got my first black toenails when I began training for a marathon, after years of running no more than three to five miles at a time. I had been wearing size 8 running shoes for my size 8 feet, and they worked fine until I increased my mileage. So when it was time to get a new pair, I went with size 8.5. After that, my toenails stopped bruising, and I also stopped getting blisters.
Your feet naturally swell a bit as you run, so it’s wise to choose shoes that accommodate this. You might think this could make your feet shift around more, but running shoes are designed to be laced tightly around the instep while still offering ample space for your toes. If you need additional support to keep your foot secure at the back of the shoe, use the extra lace holes and tie a heel lock to fine-tune the fit.
Switch your socks
If you wear thick socks, switching to thinner ones can free up some room. As an added bonus, thin socks designed for running often help prevent blisters. Consider trying Feetures or Swiftwick.
Keep your nails trimmed
Another way to prevent your nails from pressing against the front of your shoes is to keep them trimmed. Cut them to a comfortable length (but not too short, as that can be irritating) and regularly trim or file them to maintain that fit.
Perhaps paint them
That summer when I had multiple black toenails, I began exploring different nail polish colors. While bruises can show through any translucent polish, it was enjoyable experimenting with darker shades like blues and purples.
I couldn’t find a clear expert opinion on whether it’s harmful to keep bruised toenails painted. It’s not true that nails need to 'breathe' (the tissues in our toes get oxygen from our blood, not the air), but in some cases, nail polish and the chemicals used to remove it could cause the nail to dry out, or it might make it harder to tell if the nail underneath is healthy.
I can tell you that many runners paint their nails without any issues, but if you’re uncertain, it’s perfectly fine to save the nail polish for special occasions. The dark bruise will eventually grow out on its own.
Seek medical attention if they’re painful
The blood trapped beneath a bruised toenail can build up so much pressure that it causes pain. A doctor or healthcare provider can make a small puncture in the nail to drain the fluid and relieve that pressure.
There’s no shortage of guides online showing how to perform this yourself, using tools like a hot needle, paperclip, or even a drill bit. While some have attempted this, I don’t advise self-treatment. Draining a toenail is necessary when the pressure from the fluid underneath is causing pain, but it won’t help toenails that are simply mildly sore or blackened due to light bruising.
Look forward to the moment they fall off
Here’s the fun (or gross) part: sometimes injured toenails will simply fall off. They might turn black before they do, but you can also lose a toenail without any visible bruise, or the opposite might occur.
It’s not as unpleasant as it sounds, because a new nail starts growing beneath the old one. You might not even notice it until the new nail is nearly grown in. Eventually, when you go to trim your nails, you’ll see one of them lift off easily—that’s the old nail getting ready to exit.
During this awkward transition phase, you have two choices. First, if the nail is still mostly attached, use a band-aid or athletic tape to cover it, ensuring any loose edges won’t catch on your sock or shoe. Since the new nail underneath is still thin and may not cover the nail bed completely, leaving the old nail in place will protect your toe.
The alternative is to remove the old nail when it feels like the best option, rather than taping it down. You can carefully trim the nail with a nail trimmer (instead of yanking it off) and use a file to smooth any rough edges afterward.
