How to Treat a Bruised or Black Toenail from Running


Anyone who has been running for a decent amount of time has probably gotten the dreaded bruised or black toenail. Eventually, they will fall off but takes forever for them to grow back!

If you’ve found yourself in this position, the article will cover everything that you need to know about black toenails, including what they are, what causes them, ways to treat them, and how to prevent them.

What Are Black Toenails?

Let’s start with the basics and define black toenails. The proper terminology is “subungual hematoma,” but we runners all say “black toenail.” It is actually blood that collects under your toenail after an acute or chronic injury.

Black toenails aren’t always black. They can be purple or brownish, but no matter what color they actually are, it’s clear that your nail is discolored. The condition can cover the entire nail, or just a small portion of it.

How Bad Are Black Toenails, and Can They Get Infected?

Depending on the trauma to the toenail, black toenails can be mild – like something fairly tiny that doesn’t cause pain and is more cosmetic than anything. Or it can be severe, with painful and large blood blisters between the nail and nail plate.

And yes, they can get infected! The warm, moist environment inside your shoes is the perfect home for bacteria. If you have been running regularly with black toenails (especially if they are severe), you might be at risk for an infection.

What Causes Black Toenails?

There are actually several causes of black toenails, some that are more likely than others for runners. It’s important to have a good idea of what caused your black toenails. Some causes are serious and need medical attention.

Repetitive Trauma

This is the most likely cause for a runner. Black toenails can occur when your toenails are constantly taking a beating, typically the result from running on a regular basis and/or running long distances.

They can also occur as a result of wearing any type of ill-fitting footwear or loosely-laced shoes. This is especially bad if it’s coupled with running a lot. In particular, more downhill running means more bruised/black toenails as the foot slides forward.

If your toe box is too low, it will push down on the top of your nails as you push off from the ground. Shoes that are laced too tight (as opposed to too loose, which is also an issue) can compress the toenails.

When you run, your feet swell, especially on a long run and especially, especially on a long run in hot weather. If your shoes can’t accommodate the swelling, your toes bang against the front of your shoes.

In other words, if you’re putting undue stress on the toenails, that will cause repeated trauma and can lead to black toenails. Do it once, and it shouldn’t be an issue. If it’s a habit and routine, it will be.

One-Time Trauma

Unfortunately, there isn’t too much you can do to prevent black toenails from unexpected, one-time trauma. If you drop a heavy object on your foot, there’s a good chance that you’ll get a black toenail.

That being said, while it will take some time to heal, if you know that your black toenail is from dropping something heavy on it, you know that the cause is trauma and that it should be able to heal on its own. This means that it isn’t something more serious like melanoma.

Fungal Infections

Although we typically think of fungal infections as being yellow in color, which is often true, they can also turn a darker color if there is debris buildup. If your feet sweat really bad when you run, it’s the right environment for a bacterial infection.

Chronic Ingrown Toenails

If you get ingrown toenails regularly, that means that your feet aren’t getting the care that they need, which can lead to infection and/or discoloration. If the toenail changes to black, it could indicate necrosis, meaning death of cells or tissues in the toenail area.

Green Nail Syndrome

Chromonychia is more commonly known as green nail syndrome. It’s a nail disorder that is characterized by a discolored nail bed, often green/green-black. It is typically a result of chronic paronychia, or infection of the skin around the nail folds.

Subungual Melanoma

We all know that melanoma is the most serious form of skin cancer. It can grow underneath your nail bed, appearing as a dark brown spot which will make the toenail look discolored even if it’s actually underneath the toenail.

When Do I Need to See a Doctor for Black Toenails?

If there wasn’t an incidence of trauma and your nail is slowly starting to change color, then you probably should see a doctor because it’s not a trauma-induced black toenail. This is especially important if that extension of color goes beyond the nail.

If you know your shoes are too small and you’ve been running a lot or if you’ve been doing a lot of downhill running, you are probably fine to hold off on seeing the doctor to wait until things heal at home.

This should be self-evident, but if the pain is strong within hours of the trauma, there might be a more serious issue going on, so you should see a medical professional. You may also want to do so if you have an underlying condition like diabetes.

How Can I Prevent Black Toenails?

Keep Your Toenails Short

First, it’s important to keep your toenails short, especially if you run regularly. Make sure that there’s a thumb-width distance from the tip of your longest toe to the end of your shoe.

Size Up Your Shoes

If you’re a new runner, you might not realize that you really should buy a half a size up from your typical street shoe. When you purchase your next pair of running shoes, make sure there is a thumbs-width from your toe to the front of the shoe.

Like we mention earlier, your feet will swell on long runs and your shoes need to accommodate that swelling.

Pick a Wide Toe Box

Wide toe boxes are useful for ailments such as bunions. But they are also great for avoiding bruised or black toenails. With a wide toe box, your forefoot can rest comfortably in the shoe without getting pinched on the sides.

Wear Thinner Socks

It could be that you have that thumb-width of distance and there’s plenty of room in the toe box, but you just are wearing socks that are too thick. Try wearing thinner socks so that your feet take up less room in the shoe.

Wash and Dry Your Feet and Toes Regularly

Finally, the best way to avoid infections is to make sure that your feet and toes are clean. It’s important to take the time every day to wash and dry your toes. This prevents debris from collecting underneath them, and reduces warmth and moisture that are ideal for bacterial infections.

How Do I Treat Black Toenails?

While it’s great to know how to avoid black toenails, if you already have them, you’ll want to know how to treat them.

Be Patient

First, if you’re dealing with a trauma-induced black toenail, you’ll need to be patient. In mild cases, the black toenail will simply grow out. And it’s not a fast process, especially if it’s your big toe. Expect six to nine months or longer for the black toenail to grow out.

It is okay if you continue to run with black toenails (otherwise you could be out for a very long time!) as long as there is no pain. If you do feel pain, then running will make the situation worse.

Soak in Warm Water

If your toenails and/or feet feel irritated, soaking them in warm water is sure to do the trick to relieve some of that irritation. This also gives you the opportunity to wash and dry your feet and pamper them a little bit.

Use Cream for a Fungus

If you have a fungus, use an antifungal cream to treat it. You should also avoid putting your feet in situations where they’re going to be in a warm, moist environment. That favors infections. Keep them dry and ventilated to allow the fungal infection to heal.

Go to the Doctor

In the case of pain (trauma-induced or not), head to the doctor, who will poke a few holes into the nail to drain the blood. This will also relieve pressure on the toenail and can help save the nail in some cases.

Deal with a Nail Ripping Off

Finally, if you suspect that your nail is getting close to falling off or is getting really ragged, try to keep it trim so that it doesn’t catch on anything. However, if it does rip off and cause injury, you’ll want to first apply pressure until the bleeding stops.

Then apply an antibiotic ointment and cover your toenail with a bandage to prevent infection. Do this every day after showering for about 1-2 weeks. However, if possible, try to avoid this situation!

Final Thoughts

Discolored toenails are never attractive and they are sometimes painful. It’s important to know not only how to treat black toenails but also how to prevent them! Hopefully, this article has given you a good start in knowing how to take good care of your feet.

Photo of author


Ben is an avid road and trail runner, and has completed multiple marathons and ultras. A former running store owner, he now shares his knowledge and experience writing these articles.