At the end of a long walk or run, you may notice that a toenail has turned black, blue, or dark red and is getting painful. This change of colour and pain is due to bleeding under your nail, which is also known as a “subungual hematoma”. This can also happen if you drop something heavy on your toe or kick/stub your toe against something hard.
Causes of a Black Toenail or Subungual Hematoma
As you walk (particularly downhill) or run, your feet slide forward in your shoes, 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, if excessive, can damage your nail beds resulting in bleeding under the nails or creating a blister under the nail itself. When this happens, the pressure from the fluid or blood trapped by your nail causes your toenail to separate from the nail bed. This blood under your nail makes your translucent nail appear black.
When Your Black Toenail Is Painful
If the pressure on the nail has been excessive the nail may not only be discoloured but also raised and painful. If it is only mildly painful you can leave it and over time the injury will heal itself and a new nail will grow without the discolouration. (This may take up to a year to totally return to “normal”). If your toe was injured due to an accident where your toe was “crushed” it is always advisable to have it checked out at A & E or a minor injuries unit. If your toenail wasn’t crushed but is painful then a simple painless procedure performed by your podiatrist will instantly relieve the pain by relieving the pressure caused by this fluid. This will limit damage to the nail. It still will take time for the nail to return to a normal appearance.
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 podiatrist will relieve the pressure by drilling a hole or two in the nail plate (totally painless), a procedure called trephination. If you have diabetes, you should seek professional help as ulceration of the area or infection can have serious consequences.
Will I lose my nail?
Mild cases of black toenail will simply grow out. If it is a more severe case where the toenail is raised, it is likely you will “lose” the toenail. That is the nail loosened by the pressure of the fluid will eventually shed over the next weeks or months. It will gradually be replaced by a new nail either under the old damaged nail or new nail growth will gradually push the damaged nail forward as it grows. Severe or repeated injury/damage to the nail may also result in permanent changes such as thickening of the nail and ridging to the nail.
Preventing Black Toenails
Generally, prevention involves you ensuring your running or walking shoes and socks fit correctly. Your feet can swell a full shoe size over the course of a long run or walk, and your toes must have some room to expand into.
- The toe box must be wide enough so as your toes are not squashed – but not too wide.
- Your running and walking shoes must also be long enough to allow slight slippage of your feet in your shoes and as a guide the insole in the shoe needs to be approx. 1cm longer than your longest toe when standing on the insole. Remove the insoles if you can and stand on them. Make sure you check both feet and ensure this is so for your longest foot especially if one foot is larger than the other.
- The trauma of toes banging into the front of the shoe can be dramatically reduced even eliminated by proper lacing of your shoes to keep your heel in the heel counter rather than letting the foot slide forward in the shoe with each step. This is especially important if your exercise route includes uphill and downhill sections as that is when you will experience the most slippage.
If your heel slips too much or you need a little more toe room, try a lace lock at the top of your shoe. This will pull your foot back into the heel of the shoe and help stop the slippage.
Other Causes of Black Toenails
Fungal infections of the toenail can also cause colour changes in the nail from gray to blue, brown, or black. If your black toenail didn’t appear suddenly after a walk, run or workout or after dropping something on your toe, you might suspect this as a cause. You may wish to consult a podiatrist to confirm diagnosis and to discuss treatment options.
Malignant subungual melanoma
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 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 podiatrist or doctor if you are concerned that your black toenail may be a sign of this cancer.
A final word from Footfriend
Don’t despair if your walking, running or other 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. But with attention to your footwear, you should be able to have both. If you have any queries, please seek professional advice from you podiatrist.