Black toenails from running are somewhat a rite of passage for long distance athletes, a badge of honor, if you will, that demonstrates that you’re a real runner now that you’ve put in enough miles to cause the discoloration of a toenail.

At Lems, we stress the importance of proper fit of shoes and the damage that can be caused by wearing traditional footwear, so are black toenails really something to celebrate? What causes them and is footwear to blame?

What Causes Black Toenails?

As you run or hike for long periods of time, the foot slides forward in the shoe, banging against the front and sides of the shoe with each step. 

Repeated forceful contact with the front or side of the shoe creates bruising or bleeding beneath the toe bed, which is what you see when you have a black toenail. 

When the blood dries, it can cause the nail plate to separate and loosen, and can result in the toenail falling off.

In general, black toenails are not exceptionally painful, though blood blisters can be extremely sensitive to pressure as they’re forming, which can be excruciating if you hit your toe in just the right spot.

This microtrauma is caused by wearing shoes that are too small or socks that are too tight, so that’s why it is important to have your feet fitted annually and wear a foot-shaped shoe that allows the toes to splay.

Running long downhill sections or in hot weather, when the feet tend to swell, can also lead to black toenails.

How To Treat Black Toenails From Running

Most of the time, black toenails don’t need to be treated. The blood will just grow out of the nail over several months. If the toenail has fallen off, it will grow back.

If the toenail is causing significant pain, you may want to visit a podiatrist or regular doctor to drain the blood from the blister in order to reduce the pressure. You’ll want to do this before the blood dries out.

If the black toenail is not causing pain, then it’s ok to continue running as usual.

If the toenail does fall off, then clean the toe with soap and water regularly and wear a bandage to protect it while it heals. The nail will grow back over a few months.

Preventing Black Toenails

While total prevention may not be possible if you are an ultra runner or spend a lot of time in hiking shoes, it is possible to reduce the chances of getting a black toenail.

Trim the Toenails Regularly

Your nail should be flush with the end of the toe. The less beyond the skin it extends, the less chance you have of hitting the end of the shoe while you run.

Be sure to cut the nail straight across, otherwise you could be setting yourself up for painful ingrown toenails.

Wear Shoes that Fit Properly

Most traditional running shoes taper at the toe box and lift the toes up. This creates a tight space in the toe box, which can result in the toes hitting the end of the shoe more frequently.

Your running or hiking shoe should have about a half an inch of space between your toe and the end of the shoe. Many people often have to go up a half or full size to accommodate the size the feet swell to while engaging in high cardio exercise.

Wear Thinner Socks

While thicker socks may add some cushioning, they also add bulk, which can reduce the space your feet have inside the shoe. When you buy your new pair of shoes, bring along the socks you prefer to wear and try them on together to ensure proper fit.

Lace Your Shoes Differently

There are various ways to lace shoes to achieve different results in fit. Play with a few different ways and notice if you see a reduction in the number of black toenails you get.