Black Toenail From Running – Causes and Treatment

6 min read Chris Zibutis

Written by
Head Running Coach - that one person on earth who loves interval runs 🥵

Got a black toenail? Many runners experience black toenails at some point.

While unsightly, black toenails are not usually a reason for concern. However, in some cases, they can be a sign of a more serious condition.

Read on to find out what causes a black toenail and how to get rid of black toenails.

Black Toenail and Toenail Color Changes

Toenails can turn black for a variety of reasons, including trauma and underlying medical conditions.

Toenail color changes depending on what’s causing them. For example, wearing the wrong running shoes can turn your toes black within a matter of hours.

By contrast, a toenail turning black due to nutritional deficiencies or underlying medical conditions may be more gradual. It may start as discoloration under the toe followed by a bluish toenail that then becomes darker.

Trauma resulting from the impact may not turn your toenails black right away. The toenail may first become red, then purple, then dark brown. Only after the blood under the nail clots will the nail become black.

Toenail discoloration can also be whitish, yellow, purple, or green. When concerned, it’s important to see a doctor as toenail discoloration can be a sign of a serious medical condition.

What Causes Black Toenail: Common Causes and Conditions

From common bruises to fungal infections and other conditions, here’s what may cause black toenails.

Bruise under the nail

Medically known as a subungual hematoma, a bruise under the nail can develop if you wear tight shoes.

Your toe gets cramped in the front, leading to damage to the blood vessels beneath the nail. This type of bruise may also appear if you stub your toe.

Subungual hematoma occurs frequently among runners. Beginners develop it because they may not always wear the right shoes. Meanwhile, more experienced runners may have it simply because they run a lot.

Feet may swell when running because of the impact with the road. Blood flow to the feet also increases to deliver enough oxygen to the muscles. Increased blood flow can also contribute to mild swelling in the feet.

Nail fungus

Nail fungus or onychomycosis is another common cause of black under toenails.

It may begin as a white or yellow-brown spot under the nail and darken with time.

Other symptoms can include brittle, crumbly, or misshapen toes, bad smell, discoloration, and toes becoming separated from the nail bed.

Black toenail fungus may affect several toes. When it doesn’t cause pain or have other symptoms, you may not need to see a doctor. If it’s painful, though, you should see a doctor.

Ingrown toenail

A toenail may grow into the skin that surrounds the nail bed. When this happens, you have an ingrown toenail.

An ingrown toenail can cause a bacterial infection. This may change the color of the nail.

If your toe is painful and you suspect you may have an ingrown toenail, see a doctor.

Underlying medical condition

Black toenail? Diabetes and a variety of other medical conditions may have caused it.

  • Diabetes. People with diabetes have poorer blood flow to the feet. Because of this, a minor toe injury can lead to wet gangrene and a higher risk of infection.
  • Kidney disease. Kidney disease can cause discoloration in the toenails including black toenails.
  • Heart disease. Circulatory problems can affect blood flow to your toes. This can change the color of the nails.
  • Anemia. One sign of B12 deficiency anemia can be the darkening of the toenails due to hyperpigmentation. This is more common in darker-skinned people.

Melanoma

In rare cases, a black spot under the toenail can be due to subungual melanoma.

This type of cancer usually affects people aged 50–70. It’s more prevalent among African Americans, Asians, and Native Americans.

Known as a subungual melanoma, it may appear brown to black in color and have variegated borders.

If you have any concerns about a black spot under your toenail, play it safe and see a doctor.

Can a Black Toenail Cause Complications?

A black toenail caused by trauma usually heals on its own within a few months. And because it’s painless, you can keep running with it, provided you wear comfortable running shoes.

Endurance runners may experience recurrent black toenails. In some cases, the nails may fall off.

If you have persistent black toes due to intense running, you may want to take regular salt baths and keep your toes clean. This will help reduce the risk of infection.

Black toenail fungus can be more difficult to treat. It can spread to other toes or feet. It may also come back despite treatment.

A black spot under the toenail caused by melanoma is the most worrisome. Melanoma can spread to other parts of the body. But if caught and treated early, a good outcome is more likely.

How to Treat Black Toenails

The right treatment for black toenails depends on what’s causing the condition.

When it’s due to a subungual hematoma, a black toenail will slowly grow out. This usually takes at least 6 months. and the process is usually painless.

But if the subungual hematoma is painful, doctors can make a small hole in the nail to provide relief.

Known as trephination, this helps relieve the pressure that pooling blood creates under the nail. In some cases, several holes have to be made in the nail.

Through these, blood will drain out from the hematoma. With it, most of the pain will go away.

After undergoing trephination, it’s important to avoid soaking the finger or exposing it to dirt. Doing so may lead to an infection.

As we’ve seen, black toenail fungus may not require treatment. However, if it causes pain or you are concerned, you should see a doctor.

An ingrown toenail may also require a visit to the doctor. However, in some cases, you can treat it yourself.

At-home treatment includes soaking your feet in soapy water for half an hour 3–4 times a day. Applying petroleum jelly and using comfortable footwear also helps.

An ingrown toenail can be painful. If you experience pain, you may consider taking pain relievers.

When a black toenail is caused by an underlying medical condition, it’s important to address the latter. See a doctor who will adapt the treatment to your needs.

You should also see a doctor if you have a black line on your toenail or any other spot under it that you can’t explain. It may be nothing to worry about, but seeing a dermatologist can confirm it’s nothing serious.

Preventing Black Toenails

Preventing black toenails is better than having to treat them. If you run regularly, there are several things you can do to keep your toes happy.

  • Change your running shoes. Got a black toenail running long distances? Your footwear may be too tight at the front. Upgrade to better-fitting running shoes.
  • Keep your toes clean and dry. This will help prevent black toenails from fungal infections. Make sure to gently wash your feet in soapy water after a run.
  • Wear sunscreen around your toes. Enjoy running barefoot or in sandals? Don’t forget to use sunscreen. It will help prevent a black spot under the toenail from melanoma.
  • Wear shower shoes in public showers. Public showers including those at the pool or the gym can increase the risk of toenail infections. In general, it’s not a good idea to walk barefoot through public showers, bathrooms, or locker rooms.
  • Treat any underlying medical conditions. As we’ve seen, several conditions can lead to a toenail turning black. Addressing the underlying cause will help prevent or at least better manage black toenails.

When Should You See Your Doctor?

If, after reading this, you are still asking yourself, “Why is my toenail black?” you should see a doctor.

You should also see a doctor if you have a black spot on your toenail that wasn’t caused by trauma. Melanoma is rare, but it can happen. Early detection is important for proper treatment.

Of course, you should see a doctor if your black toenail is accompanied by severe pain or other symptoms. Or if you have an underlying health condition such as diabetes or kidney disease.

Even if black toenails are just the result of walking a lot, they can become a chronic problem. Seeing a doctor can provide relief and help you better manage the condition.

Takeaways

Whether you already have a black toenail or just want to prevent getting one, here are some things to remember.

  • Getting a black toenail running is normal if you wear tight-fitting shoes or run a lot.
  • A black toenail is often the result of trauma and not a cause for concern – it resolves on its own.
  • But a black spot under the toenail can indicate a serious medical condition. Have it checked by a doctor.
  • Wear comfortable running shoes, wash your feet regularly, and wear shower shoes in public showers.

In the end, don’t panic if you see a toenail turning black – most of the time it’s not serious. But don’t neglect it either. Understand what’s causing it and seek appropriate treatment.

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Chris Zibutis is the Head Running Coach and founder of Joggo – that one person on earth who loves interval runs. 🥵 He holds a degree from Copenhagen Business School and is an avid runner – having participated in numerous marathons and triathlons, Chris brings substantial fitness and running experience to the Joggo team.

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