Between common issues like toenail fungus, bunions, ingrown toenails, blood blisters, and fungal infections between the toes, distance runners don’t tend to have the best-looking feet and toenails.
And then there’s the dreaded black toenail from running, so common that it’s actually called runner’s toe.
Although most distance runners cringe in disgust when they take off their running shoes and socks and notice a blackened toenail, others see the buildup of blood under the nail bed as a badge of honor.
Runner’s toe not only looks unsightly but can be painful and may even become infected.
In this runner’s toe guide, we will discuss symptoms of runner’s toenail, risk factors and causes of black toenails from running, prevention strategies, and treatment options for blackened toenails.
What Is Runner’s Toe?
Runner’s toe, also called runner’s toenail or jogger’s toe, is the common term for the medical condition called subungual hematoma.1Tully, A. S., Trayes, K. P., & Studdiford, J. S. (2012). Evaluation of Nail Abnormalities. American Family Physician, 85(8), 779–787. https://www.aafp.org/pubs/afp/issues/2012/0415/p779.html
“Subungual” means under the toenail and a “hematoma” is a bruise, and bruising anywhere on the body is essentially blood trapped under the skin.
Therefore, a subungual hematoma refers to a condition characterized by a blackened toenail or similar discoloration (blue, purple, or dark red) due to a buildup of pooled blood under the toenail that has leaked out from broken blood vessels that feed the nail bed.
If the damage to the blood vessels is significant, nutrients won’t be able to perfuse the nail bed and the toenail will eventually die and then fall off.
Eventually, a new nail will grow.
Despite having the name runner’s toe, athletes other than long-distance runners can suffer from subungual hematomas, including soccer players, racquetball players, or any sport where the nail of the big toe or other toes repeatedly slams against the inside of the shoe or experiences constant pressure.
In fact, runner’s toe is also called tennis toe since this condition is also prevalent among tennis players.2Thompson, K. (2023, April 18). Tennis Toe: Causes, Prevention and Treatment. North Central Surgical Hospital. https://northcentralsurgical.com/tennis-toe-causes-prevention-and-treatment/#:~:text=Also%20known%20as%20%E2%80%9Crunner
What Causes Runner’s Toe?
Many people assume that distance runners are prone to foot pain and more serious running injuries given the high-impact, repetitive nature of running.
While it is true that distance runners who have poor biomechanics,3Willwacher, S., Kurz, M., Robbin, J., Thelen, M., Hamill, J., Kelly, L., & Mai, P. (2022). Running-Related Biomechanical Risk Factors for Overuse Injuries in Distance Runners: A Systematic Review Considering Injury Specificity and the Potentials for Future Research. Sports Medicine. https://doi.org/10.1007/s40279-022-01666-3 wear the wrong running shoes, wear orthotics,4van der Worp, M. P., ten Haaf, D. S. M., van Cingel, R., de Wijer, A., Nijhuis-van der Sanden, M. W. G., & Staal, J. B. (2015). Injuries in Runners; A Systematic Review on Risk Factors and Sex Differences. PLOS ONE, 10(2), e0114937. https://doi.org/10.1371/journal.pone.0114937 increase mileage too quickly,5Quinn, T. J., & Manley, M. J. (2012). The impact of a long training run on muscle damage and running economy in runners training for a marathon. Journal of Exercise Science & Fitness, 10(2), 101–106. https://doi.org/10.1016/j.jesf.2012.10.008 or make a variety of other training errors are at risk of foot pain and running injuries, more minor running injuries—such as those to the toenails or nail bed—are far more common.
In fact, a survey of 719 trail runners found that toenail injuries were the most commonly reported injuries amongst the runners, with 24.8% (nearly 1 in 4!) of the runners noting runner’s toenail, a toenail falling off from running, or another toenail injury in the past 12 months.6MATOS, S., SILVA, B., CLEMENTE, F. M., & PEREIRA, J. (2021). Running-related injuries in Portuguese trail runners: a retrospective cohort study. The Journal of Sports Medicine and Physical Fitness, 61(3). https://doi.org/10.23736/s0022-4707.20.11304-5
Runner’s toe is primarily caused by repeated stress on your toenails as you run, either by way of pressure from the top of the running shoes or from small but repetitive slams into the end of the running shoes.
Runner’s toe is most common in the big toe (first toe) or the longest toe, which is often the second toe.
This is because the big toe is often the largest toe and often the longest or nearly the longest toe, and it is the main toe used for push-off during the gait cycle.
Therefore, it can be more cramped in the toe box of your running shoes, and the accumulated pressure buildup on the toenail and nail bed at push-off can injure the blood vessels feeding the nail.
The second toe is often the longest toe, so it is prone to ramming against the inside end of the toe box of your running shoes.
Essentially, the main cause of black toenails from running is accumulated microtraumas on the toenail during the gait cycle rather than one acute misstep like accidentally taking a swift kick to a big rock or tripping on a curb.
Generally, this most likely occurs either at ground contact if your foot slides forward in your running shoes and the tips of your toenails slam into the inside of them, or at push-off when the big toe is extended and rubs against or is pressed on the inside of the toe box.
Another cause of black toenails after running is a blood blister under toenails, which usually results from repetitive friction over damp or sensitive skin.
For example, your toenail might be shearing back and forth against the top surface of the inside of your running shoe as you run.
Because you take thousands of steps per run, these microtraumas accumulate enough to damage the blood vessels under the toenail that supply the nutrients the nails need to survive.
This can result in pooled blood under the nail that is visibly seen as a black toenail or a bruised, purple, or blue toenail, and it can also cause the toenail to eventually fall off because the nutrient supply is damaged.
There are other potential causes of blackened toenails or pooled blood under the nail while running.
Here are some other possible causes of black toenails after running:
- Fungal infections
- Anemia (low iron)
- Diabetes
- Heart or kidney disease
- Melanoma
It is advisable to consult your healthcare provider if you have concerns about any of the above conditions.
What Are the Symptoms of Runner’s Toe?
The most common signs and symptoms of runner’s toe include dark discoloration of the toenail (usually the first or second toe), pain and tenderness, pressure under the toenail, a loosening of the nail from the nail bed, and the toenail falling off.
There’s also a risk of infection, particularly before the new nail grows in, which can take 6-9 months.
Signs of infection include redness, warmth, swelling, more intense pain, and drainage or pus.
How Can I Prevent Black Toenails From Running?
Although some runners see a black toenail after running as a badge of honor, runner’s toe is indeed a running injury and can interfere with your training due to foot pain, particularly if your toenail becomes infected.
As a running coach, these are the top tips I have discovered to be most effective at preventing black toenails from running:
- Regularly trim your nails so that they stay neat and short and don’t extend beyond your toes.
- Clip your toenails straight across, rather than in a curve to prevent ingrown toenails.
- Wear running shoes that are the right size both in terms of the length, width, and shape of the toe box. You should have about a thumb width’s distance between the end of your longest toe and the tip of the running shoe, and you should be able to wiggle your toes comfortably within the toe box to accommodate foot splay.
- Wear moisture-wicking socks with a seamless toe and ample cushioning.
- Lacing your shoes tight enough so that your foot stays in place without sliding forward. You can experiment with different lacing techniques.
- Avoiding excessive downhill running.
- Put moleskin pads or silicone pads on the tips of your big toe and second toe before you run if you still keep getting bruising or painful toenails after running.
- Bunions can be a risk factor for runner’s toe, so make sure you wear shoes with a wide enough toe box (even daily shoes aside from running shoes) to prevent bunions.
How Do You treat Runner’s Toenail?
If you have pain and swelling with runner’s toe, you can use the RICE treatment protocol, which stands for Rest, Ice, Compression, and Elevation.
To prevent infection after your toenail falls off, soak the affected foot in warm salt water several times per day and wear clean, dry socks.
Cover the nail bed in a light, protective dressing such as a sterile Band-Aid or gauze.
You may need to reduce your mileage by either taking time off or doing low-impact cross-training until your toenail pain resolves, especially if you get an infected nail bed.
If you are concerned that your nail isn’t healing or you have an infection, seek medical care from your doctor, podiatrist, or someone who works in dermatology.
Nail trephination,7Pingel, C., & McDowell, C. (2024). Subungual Hematoma Drainage. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482508/#:~:text=The%20injury%20may%20also%20be in which a sharp needle is used to drill a small hole through the nail plate to allow the pooled blood to be released may be necessary to relieve pressure.
Additionally, working with a running coach to ensure you are using good running form and wearing proper shoes can be a great way to earn medals as your badges of honor…not black toenails!
If you enjoyed this guide, check out our next one on blisters:
I’ve been suffering from it , and the article is very informative Thank You so much for sharing !
Glad it was helpful!