Black Toenails From Running or Walking

Black Toenail
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In This Article

At the end of a long walk or run, you may notice that a toenail has turned black, blue, or gray, and it may be swollen under the nail. You are getting a black toenail due to bleeding under your nail, which is also known as a subungual hematoma. This can also happen if you drop something on your toe or smash your toe against an object.

Causes of a Black Toenail or Subungual Hematoma

As you walk or run, your foot slides forward in your shoe, banging your toes against the top, front, and sides with each step. Your feet also swell during a walk or run and get compressed by your socks and shoes. That pressure and impact can damage your toenail beds, or create a blister under the toenail itself. When this happens, the extra blood and fluid cause your toenail to separate from the toenail bed. The blood colors the toenail black and your toenail will probably continue to change colors during the course of healing.

When Your Black Toenail Is Painful

If there is a blister under the toenail, you may see the toenail raised and it may be swollen and painful. It is best to try to ignore this for 24 hours and see if it goes down by itself. No treatment is needed unless the nail is raised and painful after 24 hours. Nature will take its course and you should simply leave it alone.

If the nail is still raised and painful after a day, you may want to see a doctor. If your black toenail happened due to an accident where your toe was crushed, you should see a doctor so it can be checked for other injuries.

Treatment for a Black Toenail

There is no need to drain a black toenail that isn't raised and painful. If the problem is simply a pool of blood under the nail and it continues to be raised and swollen, then a doctor would relieve the pressure by poking a hole in the nail, a procedure called trephination. Although it's preferred that a professional does this, it is something that some people do at home themselves. If you have diabetes, you must seek medical help rather than draining it at home as an infection can have serious consequences.

You can see this self-treatment described by marathon coach Jeff Galloway and in the book "Fixing Your Feet: Prevention and Treatments for Athletes" by John Vonhof, Wilderness Press, 2011.

If the toe continues to be swollen and red after draining the excess fluid, see a doctor to check for infection.

Take infection seriously. If it continues to hurt or the pain increases, this is a bad sign. Toe infections can lead to blood infections, gangrene, and worse, especially if you have diabetes.

Losing Your Toenail

While minor cases of a black toenail will simply grow out, if the toenail is raised it is likely you will lose the toenail. It will take a few weeks or months, but as the toenail continues to grow, eventually it shoves out the damaged, blackened toenail. The black toenail is raised off of the toenail bed and underneath it is often the healthy remainder of your toenail. Your black toenail will gradually loosen from the sides and you will be able to trim it away.

If pretty toes are important to you, you can paint the black toenail or even the new thin toenail or the bare skin. Most people won't notice the difference if you use a darker shade of polish. Black polish and darker shades may be in fashion.

Full replacement of your toenail takes about three months, and the new toenail will often be a bit wavy—thin in some areas and thicker in others. After four to five months your toenail should be back to normal.

Preventing Black Toenails

Your running or walking shoes and socks must fit correctly. Your feet swell a full shoe size over the course of a long run or walk, and your toes must have someplace to expand into. The toebox must be wide enough, yet not too wide or your toes will bang around in it. Getting fit for your athletic shoes at a technical running shoe store in your area is your best method of ensuring your shoes fit correctly.​

The trauma of toes banging into the shoe can be eliminated by proper lacing of your shoes to keep your heel in the heel box rather than letting the foot slide forward in the shoe with each step. This is especially important if your exercise route includes uphills and downhills as that is when you will experience the most slippage.

Other Causes of Black and Blue Toenails

Fungal infections of the toenail can also cause color changes in the nail from gray to blue, brown, or black. If your black toenail didn't appear suddenly after a workout or after dropping something on your toe, you might suspect this as a cause. Over-the-counter anti-fungal treatments are available, but you can see your doctor if these are not effective after a few weeks.

A rare cause of black toenail is malignant subungual melanoma. Unlike trauma to your toenail, this does not appear suddenly but you will see a black line or band extending up to the nail from the cuticle. One difference between this type of cancer and common toenail trauma is that the black line extends into the cuticle. See your doctor if you are concerned that your black toenail may be a sign of this cancer.

A Word From Verywell

Don't despair that your fitness activities are hurting your toes. It is a signal that you need to be more careful in selecting your footwear and lacing it correctly. You might change your mindset and know that a healthy body is better than pretty toes. But with attention to your footwear, you should be able to have both.

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Article Sources

  1. Pingel C, McDowell C. Subungual Hematoma Drainage. [Updated 2019 May 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.

  2. Levit EK, Kagen MH, Scher RK, Grossman M, Altman E. The ABC rule for clinical detection of subungual melanoma. J Am Acad Dermatol. 2000;42(2 Pt 1):269-74. doi:10.1016/S0190-9622(00)90137-3

Additional Reading

  • Subungual Hematoma, American Osteopathic College of Dermatology.
  • Vonhof J. Fixing Your Feet: Prevention and Treatments for Athletes Wilderness Press, 2011.