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What Causes Black Toenails?

Sheryl Butterfield
Updated Mar 03, 2024
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Black toenails are caused by trauma to the nail. Common causes of toenails turning black include ill-fitting shoes, fungus, dropping an object on the toe and cutting the nail too short. Impact to the toenail causes bleeding underneath the nail's surface. Part or all of the toenail may turn black. Subungual hematoma is the medical term for black toenail, literally meaning "blood underneath a nail."

Athletes often suffer from black toenails, especially those who run on hills or play soccer. A shoe without enough space for the longest toe, usually one thumbnail length, is to blame. When the toe rams into the shoe or the foot slides around, blood is pushed back under the nail with each step or kick. Athletes can wear socks that wick away sweat to prevent sliding.

Clipping toenails straight across at a moderate length lessens the chance of ingrown toenails, which can lead to black toenails. When the sides of the nail dig into the skin, folds cover the nail as it grows. Tight-fitting shoes can also cause ingrown toenails. The pressure can break the skin, leaving it open to infection and discoloration from blood.

Another cause of black toenails is fungus, or onychomycosis. This common fungus begins with white spots and can advance to thick, yellow toenails. Again, ill-fitting shoes rub tiny breaks into the nail, leaving it open for infection from foot perspiration. Typically affecting the big toe, this fungus puts pressure on the toe, causing painful inflammation.

Athletes are at risk for fungus because it thrives in a warm, moist shoe. The elderly and diabetics are also at risk. Mild fungus is easily treated with an antifungal, over-the-counter oral medication. Prescription topicals are available at a higher cost, but may be a safer choice for diabetics with a moderate case. More advanced, repeated cases may require laser treatment, where a laser kills the pathogens which started the infection.

Black toenails are mostly harmless. Sometimes, in painful situations, the liquid underneath the toenail needs to be drained or the nail removed. Often, however, black toenails simply fall off and a new toenail grows in.

A rarer cause of a discolored toenail is melanoma. Malignant melanoma in the foot is easily treated if diagnosed early. In instances of trauma, the discoloration is underneath the toenail and moves with the nail as it grows. If no trauma has occurred and no fungus is present, a podiatrist should evaluate the nail soon after discoloration appears. The doctor may request a biopsy to confirm suspicions.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Sheryl Butterfield
By Sheryl Butterfield , Writer
Sheryl Butterfield, a freelance writer in Denver, Colorado, is dedicated to addressing contemporary issues in her work. With a keen interest in environmental conservation and renewable energy technologies, Sheryl crafts informative articles that educate and inspire readers. She also provides practical advice for parents navigating the challenges of raising teenagers, drawing from her own experiences and research.

Discussion Comments

By orangey03 — On Oct 21, 2012

Did you know that there is such a thing as antifungal nail lacquer? I found this out after I got an infection that caused me to have thick black toenails.

My doctor gave me pills and an antifungal topical cream. However, she said that I should prevent the infection from coming back, too.

That's when she told me about the nail lacquer. It's like regular nail polish, but it is able to prevent fungus from invading. It is available in many shades or in clear.

By cloudel — On Oct 20, 2012

@wavy58 – Keeping your toenails painted black is a good idea! I wish I had thought of that after I dropped a heavy box on one big toenail.

Instead, I just let it go. It eventually cracked right across the middle, and I was able to pull it off slowly.

I get queasy even thinking about pulling off the majority of a black toenail, but once I saw that it wasn't going to hurt at all, I was able to remove it. Amazingly, I had no feeling in the black toenail.

By wavy58 — On Oct 20, 2012

I accidentally dropped a car tire on both of my big toes, and I had two black toenails a little while later. This was in summertime, when I would be wearing flip-flops and open-toed shoes, too.

I hide the ugliness by painting my toenails black. When the two offending toenails fell off, I just removed the paint from my other toenails and wore them plain so that they would better match the skin of my nail bed that was exposed on the big toenails.

By Perdido — On Oct 19, 2012

It is important that you check the fit of your child's shoe from time to time if he or she plays soccer. Some kids grow rather quickly, and this may be one of the many black toenail causes.

My nephew hit a growth spurt around the age of ten, and he was on a soccer team at this time. Before he knew it, his toes were hitting the end of his shoes, and he developed painful black toenails.

Once his mother figured out what was going on, she bought him some new shoes. She had to monitor his growth closely, in case he outgrew those and started having the same issue again in a short period.

By widget2010 — On Jan 19, 2011

Most types of treatment for black toenails or other toenail abnormalities, like ingrown nails, are more trouble that they are worth. From my experience, making sure you trim nails regularly and keep them disinfected can prevent things like fungus or ingrown nails.

As for black toenails, if it happens regularly it could be a problem of shoe fit or something along those lines, though usually it is a one-time thing that you just have to get over.

By subway11 — On Jan 19, 2011

For me whenever I experience a toenail infection like black on toenail it was due to tighter fitting sneakers when I jog.

As a runner you can't stop when you feel a little pinching sensation on your nail because it will hurt your workout results, and if you continue when you finish your run you will notice that the affected nail will become red and discolored until it eventually gets black.

It has not happened to recently because I make sure that my sneakers fit comfortably. I have never looked at how to treat black toenails because eventually the nail falls off and a new nail will grow in its place.

I know that there are black toenail treatments but I have never looked at them.

Sheryl Butterfield

Sheryl Butterfield


Sheryl Butterfield, a freelance writer in Denver, Colorado, is dedicated to addressing contemporary issues in her work....
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