What to Do When Running Gives You Black Toenails

What to Do When Running Gives You Black Toenails
Photo: fizkes, Shutterstock

If your feet hurt on short runs, you probably just aren’t wearing the right shoes. But it’s common to start getting toenail problems when you start increasing your mileage, like training for a marathon. Here’s what to do if you’re getting black toenails, or worse.

(What’s worse than black toenails? It turns out that toenails can fall off if they’re subject to enough injury. If this has never happened to you, you’re probably absolutely disgusted right now. If it has — and I’ve been there — you know that it’s actually not that big a deal, and they grow back. But more on that in a sec.)

Why do toenails turn black?

Typically, a black (or blue, or purple) toenail is just a bruise that you can see because your toenail is clear. That’s what we’ll be talking about today. These bruises can happen suddenly — like if you drop a weight plate on your toe — or they can occur as you bump your toes into the front of your shoes thousands of times each mile.

There are other reasons that a toenail can change colours, several of which are explained in this Runner’s World article. Those include normal pigmentation changes that can happen over time, different types of toenail fungus, and even some types of skin cancer. A colour change that extends beyond the nail, for example, is cause for concern; so is a black spot that stays in place for months rather than growing out or fading away. But usually, if you’ve upped the mileage and your toes start turning black, the cause is the obvious one.

Size up your shoes

While bruised toenails are common among people who run a lot, they are by no means inevitable. If your toenails are bruising all the time, your shoes are probably too tight in the toebox.

I got my first black toenails when I started training for a marathon, after years of never running more than three to five miles at a stretch. I had bought size 8 running shoes to fit my size 2.44 m, and for all those years they had been fine. But when it was time to buy a new pair, I upgraded to an 8.5. My toenails stopped turning black, and as a bonus I stopped getting blisters, too.

Your feet swell a little bit as you run, so it’s smart to buy shoes that account for it. (As long as you keep the laces snug around your instep, the shoes won’t slide around.) You may not need the extra room on short runs, but once you’re covering serious mileage, that half size makes a big difference.

Change your socks

If you run in thick socks, switching to thinner ones can buy you some space. As a bonus, thin socks made specifically for running will often make your feet less blister-prone.

Trim your nails

Another way to stop your nails from pushing into the front of your shoes is to keep them trimmed. Cut them as short as is comfortable (too short can be irritating as well), and trim or file them frequently to keep them that way.

Paint them, maybe

The summer I had all those black toenails, I started shopping for interesting colours of nail polish. Bruises will show through anything sheer, but it was fun to experiment with dark colours, including blues and purples.

I couldn’t find an expert consensus on whether or not it’s bad to keep bruised toenails painted. It’s not true that nails need to “breathe” (the tissues in our toes get their oxygen from our blood, not from the air directly) but in some cases nail polish and the chemicals we use to remove it can contribute to the nail drying out, or they can simply make it harder to see whether the nail underneath is healthy.

I will say that plenty of runners paint their nails with no ill effects, but if you have any doubts, it’s also fine to save the nail polish for special occasions. The dark colour of the bruise will grow out eventually.

Seek care if they hurt

It’s possible for the pooled blood under a bruised toenail to cause so much pressure that it hurts. A doctor or other provider can puncture the nail to drain fluid and relieve the pressure.

There is no shortage of instructions on the internet for how to do this yourself, using a hot needle or paperclip, or even a drill bit. While people have done this, we don’t really recommend self-surgery. In any case, draining a toenail is for when the pressure from fluid under the nail is causing pain. It won’t do anything for toenails that are painless or mildly achy after turning black from mild bruising.

Look forward to when they fall off

This is the fun/gross part: injured toenails sometimes fall off. Sometimes they’ll turn black and then fall off, but you can also have nails fall off without an obvious bruise, or vice-versa.

It’s less gross than it sounds, because a new nail starts growing underneath the old one. You may not even notice what’s happening until the new nail is already mostly in place. You’ll just go to trim your nails one day and notice that one of them lifts up easily — that’s the older, top nail getting ready to make its exit.

This transition period can be awkward, and you have two choices. First, if the nail is still mostly attached, use a band-aid or athletic tape to cover the toenail, making sure that any loose edges won’t catch on your sock or the inside of your shoe. Since the fresh new nail underneath is thin and may not yet cover the entire nail bed, keeping the old nail on will help to protect your toe.

The other option is to remove the old nail, which you can do as soon as it feels like that’s a better option than taping it. Consider using a nail trimmer to do the job carefully (rather than yoinking and hoping for the best), and then use a file to smooth down any rough edges.

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