I ran for roughly 10 years and kept all my toenails . . . until I didn’t. Although there are causes for black toenails (and we’ll get into that), much like chafing, it can be totally random.
What is a black toenail?
Black toenails can have many causes, but for runners, it’s usually caused by blood underneath the nail (technically a subungual hematoma). That blood puts a great deal of pressure on the toenail, and it can be very painful.
I was lucky: although I felt some pain, it wasn’t horrible, and I just assumed that it was a blister. It wasn’t until after I stopped running that it got really painful, but thankfully by the next morning it didn’t bother me that much.
What causes a black toenail?
The most common cause is repetitive trauma to the nail, either from the top of your shoe rubbing it or from your toenail slamming into the front of your shoe. In my case, I was wearing shoes I’d already worn in another half marathon (a steep downhill race, no less) with no issues.
The downhill race was much hotter, but also much less humid. Your feet do swell as you run, and more humid conditions will make them swell more — still, it was a pretty big shock to me when I took my shoes off.
How to treat black toenails
Follow Hippocrates advice: first do no harm. Leave it alone. Depending on the severity of the hematoma, there’s a chance that you’ll keep the nails — but most likely at some point the toenail will detach from the nail bed and you’ll lose it.
That’s what happened to me. I left it alone. I hoped I’d keep the nail, but I didn’t. It actually took almost a month before it fell off. It felt fine, was still black, and then one day it was just barely hanging on. I didn’t want to pull it, so I ended up just snipping the few remaining points that were hanging on.
What if it’s really, really painful?
It will be really, really painful the day it occurs; afterwards the pain should decrease rapidly. If it’s still really painful, or if you see signs of infection (redness, hot to the touch), then it’s time to seek a doctor’s help.
How can I avoid black toenails?
The first thing you can do is make sure your shoes fit properly. Even if you’ve been fitted for running shoes in the past, it’s not a bad idea to get fitted every year. Your foot can change — even gaining or losing weight can cause changes.
Keep your toenails trimmed — although don’t do it in the days right before a race — those sharp toenail corners can cause problems, too. A week or two before your race (depending on how fast your nails grow) make sure they’re clipped (I always do this!).
Increase training distance gradually so that your toes can adjust to the new distance.
Don’t run faster than your prescribed training paces and much like distance, increase pace gradually.
Will my toenail grow back?
In a word: yup. I was quite surprised that when my toenail finally detached, roughly a month later, there was already a new (tiny) toenail underneath it.
Black Toenails: Final Thoughts
Most runners who run longer distances will get a toenail at some point in their running career — maybe many. Some lucky runners will never lose one (I was in that camp for a long time!).
You know how they say pain is temporary and PRs are forever? The pain of a black toenail is also temporary. It may even signal a PR for you, or a new longer distance for you (sadly, neither was the case for me).
You can definitely take steps to avoid black toenails, but much like anything in life, they’re unpredictable, so forewarned is forearmed.