The terms black toenail, runner’s toe, tennis toe, or toenail subungual hematoma all describe the same condition and are interchangeable. It results from bleeding in the nail bed, just underneath the nail, and appearing black. It can occur by direct trauma to the toe or repetitive trauma from the toe friction, as occurs with walking or running.
The terms black toenail, runner's toe, tennis toe, and subungual hematoma are all the same condition.
A black toenail occurs when blood from the nail bed stays under the nail plate.
A black toenail can be caused by direct trauma (from a heavy object), crush injury, or cumulative trauma from a repetitive action like the toe repeatedly making contact with the sneaker in a sport like running.
Properly fitted footwear and sport-specific footwear are essential to prevent black toenail.
Anatomy of the nails
Learning the nail structures is essential in understanding a subungual hematoma or black nail.
As shown above, the nail area is made up of several important structures:
- Nail plate. The nail plate is what we colloquially call the nail. It is composed of a hard substance called keratin.
- Nail bed. The nail bed is under the nail plate. It is comprised of a deeper layer, the dermis, and an outer layer called the epithelium, a "sticky" substance for adherence to the nail plate.
- Nail matrix. The nail matrix is the part that produces new nail plates, a process that takes about 18 months for an entirely new nail.
How is a black nail formed?
When the nail bed is injured, it will bleed. The blood then becomes trapped between the nail bed and the nail plate, leading to the black areas under the nail.
Blood entering this space causes pressure and pain since nerve endings are compressed.
Causes of subungual hematoma
Subungual hematomas can be caused by trauma including:
- Direct blow. A common example would be dropping a heavy object on the toe.
- Crush injury. For example, getting your toe trapped in a door.
- Cumulative trauma. This occurs in a person who walks or runs frequently. Subungual hematomas occur due to the repetitive friction between the toes, sneakers, and other toes. This cumulative trauma leads to pressure on the nail bed, causing it to bleed. It is also seen in hikers since the downhill portion of the hike places stress on the toes.
Having a toenail fungus increases the likelihood of developing a black toenail.
A physical exam to inspect for the following:
- A toenail fungus producing a yellow and rough textured nail.
- To check if the nail is still being held in place or no longer attached to the nail bed, a condition called an avulsed toenail. The avulsion can be partial or complete.
- Check if the toe tissue is still attached or missing.
After examining the toe, your provider may order x-rays of the toe to evaluate for an underlying bony fracture, called a tuft fracture, when it occurs at the furthest end of the bone.
If the subungual hematoma is less than 48 hours old, a simple trephination procedure can be performed, in which a small hole is made in the nail to allow the blood to evacuate from under the nail, relieving the pressure and pain.
The trephination can be done with a needle, however, it is more often done with an electrocautery device — an electric current generating a heated filament to enable the user to burn a tiny hole.
How to prevent a black toenail
To prevent non-traumatic subungual hematoma (black toenail) there are a number of recommendations to consider:
Proper fitting sneakers (shoes)
Properly fitted sneakers are essential, since you don't want sneakers that are too small or too large. Furthermore, there should be some space at the end of the toes, but not enough to allow foot movement inside the footwear. We recommend having a professional measure your foot for size, width, and arch. In addition, a professional can help you decide which brand to choose, since different brands are better for different-shaped feet.
Sport specific footwear
Running or jogging while wearing tennis shoes is not a good idea.
Tie the laces with the correct tightness
You want to tie your laces so the sneakers (shoes) are snug but not too tight — this is especially important for hikers when walking back down the trail. If the laces are too loose, the toes can repeatedly contact the front of the sneaker, leading to a black toenail.
Keep your toenails trimmed
If your toenails are too long, the toe is more likely to experience repetitive trauma from friction.
Choose the proper orthotics (inserts)
Some custom or prefabricated orthotics could raise the toes or push them forward, increasing friction and the risk of a black toenail.
We recommend you wear socks for running and long walks. Some socks are great at absorbing moisture, others push the moisture away from the foot, and some are good for shock absorption. All these socks decrease toe friction.
Change your socks
After a long walk or run, it's a good idea to take off your socks, rinse your feet, and place on a new pair of socks. This process decreases your chance of developing a fungal infection, colloquially called athlete's foot. Sometimes, a foot fungus can lead to a toenail fungus (yellow toenail), increasing the risk of developing a black toenail.
Silicone toe pads
These can help decrease friction and absorb shock.
How you walk can be reviewed by a specialist who analyzes gait — a person's walking pattern. Furthermore, a physical therapist or other specialists can evaluate your running technique.