One thing you probably werent thinking of?

Toenails that turn black and, in some cases, even fall off.

Heres everything it’s crucial that you know about black toenails in runners.

Black toenail from running

Aitor Diago

How can running turn your toenails black?

It basically causes bruising or bleeding underneath the toenail in the bed of the toenail.

That black color you see is really the dried blood, he explains.

Oftentimes, it doesnt hurt, says Dr. Lucas.

It’s not like the obvious, stop-in-your-tracks pain you feel when you drop something on your foot.

The more blood under the nail, the more it’s going to hurt.

In most cases, you dont need to do anything for a black toenail.

Treatment for black toenails brought on by running simply depends on how much pain theyre causing you.

For black toenails causing lots of pain, though, see your podiatrist.

(Definitely do not try this at home.)

(If its bleeding when it falls off, apply pressure first to stop it.)

Heres how to reduce your chances of getting the dreaded black toenail.

First, keep your toenails shortthe nail should be flush with the end of your toe.

(Just confirm to cut straight across.

Leaving curves or sharp edges can leave you vulnerable to aningrown toenail, says Dr. Lepow).

Then take a close look at your running shoes.

Shoes that are too tightespecially those that pinch in the toe boxcan make that repetitive trauma more likely.

(Determine this while you are standing, not sitting, so your toes are fully forward.)

Your socks play a role too.

(The experts at a running store can help you make the right choice.)

Heres when black toenails may indicate something more serious.

While black toenails due to running are generally harmless, its possible that something else is going on.

Having a doctor check outanypigmentation change on your skin is always a smart idea.

According to a study published inDermatology,melanoma under the nail makes up only 3% of all melanomas.

In fact, you may even see pigment spreading to the tissue surrounding the nail, says Dr. Lucas.

Its also possible that blackening under your toenails can simply be a natural pigment change as you get older.

So if you run oftenespecially if youve recently upped your mileageand notice a black toenail, dont freak out.

Chances are the repetitive trauma of pounding the pavement is to blame.

And its still a good idea to loop in a doctor so they can monitor and help treat it.