There’s a moment, usually a few days after a long run or race, where you take your socks off and think: “that doesn’t look right.”

Welcome to endurance running.

Black toenails (and the occasional full nail departure, which is always a lovely surprise) are one of those things nobody mentions when you start training seriously. You hear about pacing, nutrition, shoes, maybe even recovery. No one says: “by the way, your toes might start slowly exiting the sport.”

From what most of us eventually figure out the hard way, it usually comes down to repeated impact and pressure inside the shoe. On long runs especially, your foot subtly slides forward with every step. Even if you think your shoes fit well, fatigue changes mechanics. Your stride gets a bit sloppier, your foot swells slightly, and suddenly your toenails are getting repeatedly tapped, pressed, and generally bullied from the inside.

If I understood my podiatrist correctly, it’s basically persistent micro-trauma, until the nail gives up and either turns black from bruising and/or falls out entirely.

Watt I’ve Learned

Start with different shoes. Probably slightly bigger, and try different models and brands. Sometimes this helps or at least makes it less worse.

Also try lacing properly. Heel lock, runner’s knot, basically telling your foot it is not allowed to move forward in space. This actually helps more than you expect, because reducing forward slide of course reduces impact.

Another often neglected one is, quite simply, your socks. Thicker, thinner, double-layer, “aero socks” (yes, they are a thing). Socks help a bit with friction.

I got rid of the yellow/black/no toe nail situation almost entirely with adjusting the above three. Your running shoe size can be significantly bigger than your standard shoe size. If possible for you, go to a specialist running store, where they can test your run and figure out what shoe would work best for you. Shoes with enough toe box space so your nails aren’t constantly pressed against the front are massive. Getting your lacing tight enough around the midfoot so your foot doesn’t slide forward on descents definitely also does some lifting. And, in case not obvious, of course keeping toenails trimmed short enough helps as well. And, if you’re running long and downhill-heavy routes, be extra careful.

But even then, keep in mind that for some of you, the risk never really goes to zero. You can reduce the chances. You can optimise, adjust, and fine-tune. But black toenails are most probably part of the sport in the same way that rain is part of racing in Belgium.

If you found some miracle cures that worked very well, please drop a note in the comments, I’m genuinely curious to hear about this.