Running isn’t the only culprit.
By Jenny McCoy, Runner's World
Many runners are all too familiar with black toenails. The condition involves bruising, blistering, or bleeding beneath your nail from repetitive trauma, either from the top of your shoe rubbing against your nail or your toe slamming into the end of your shoe. It’s most commonly experienced by marathoners and those training at especially high intensity. Some even see it as a badge of honor—the more black nails you have, the more badass you are.
But not all black toenails are caused by running, and in certain cases, one can signal something more serious. Here’s how to identify which ones you need to worry about and which ones are totally harmless.
Many runners are all too familiar with black toenails. The condition involves bruising, blistering, or bleeding beneath your nail from repetitive trauma, either from the top of your shoe rubbing against your nail or your toe slamming into the end of your shoe. It’s most commonly experienced by marathoners and those training at especially high intensity. Some even see it as a badge of honor—the more black nails you have, the more badass you are.
But not all black toenails are caused by running, and in certain cases, one can signal something more serious. Here’s how to identify which ones you need to worry about and which ones are totally harmless.
Repetitive Trauma
The most common culprit for black nails is repetitive trauma, which can result from running or from wearing any type of ill-fitting footwear. If a black nail crops up shortly after a workout or a day spent in too-tight or too-loose shoes, this is likely the cause.
Repetitive trauma ranges from mild (think: a small, painless, black-and-blue discoloration beneath the nail), to severe (large, bloody blisters between your nail and nail plate), explains podiatric surgeon Jacqueline Sutera, D.P.M. In mild cases, no treatment is needed, and the black nail will simply grow out.
In severe cases, beneath-the-nail blisters can cause the nail to detach—either partially or fully—from the nail plate. This process can be quite painful if the detachment is only partial, warns sports podiatrist Lori Weisenfeld, D.P.M. She explains that once the nail fully separates from nail plate, it is officially dead and will never reattach. The good news is that it’s no longer painful. The bad news? It can take a long time for a new nail to grow in—about a year for big toenails and three to six months for smaller nails. In certain cases, a fresh nail can begin growing underneath an old, dead nail.
If there’s additional repetitive trauma, the new nail can become bruised and detached as well. To prevent this, Weisenfeld recommends visiting your doctor who can trim down or entirely remove the dead nail, which will allow the new nail room to grow in properly.
Another time you should visit your doctor is if the skin surrounding your blackened nail is red, inflamed, or oozing. This may be a sign of an infection, Sutera says, and you should apply an antibiotic ointment until you can get an appointment.
To avoid black toenails caused by repetitive trauma, Jordan Metzl, M.D., a sports medicine physician at the Hospital for Special Surgery in New York City, recommends either trying a bigger shoe or wearing a thinner sock (thick socks may cause too much pressure on your toenails).
Repetitive trauma ranges from mild (think: a small, painless, black-and-blue discoloration beneath the nail), to severe (large, bloody blisters between your nail and nail plate), explains podiatric surgeon Jacqueline Sutera, D.P.M. In mild cases, no treatment is needed, and the black nail will simply grow out.
In severe cases, beneath-the-nail blisters can cause the nail to detach—either partially or fully—from the nail plate. This process can be quite painful if the detachment is only partial, warns sports podiatrist Lori Weisenfeld, D.P.M. She explains that once the nail fully separates from nail plate, it is officially dead and will never reattach. The good news is that it’s no longer painful. The bad news? It can take a long time for a new nail to grow in—about a year for big toenails and three to six months for smaller nails. In certain cases, a fresh nail can begin growing underneath an old, dead nail.
If there’s additional repetitive trauma, the new nail can become bruised and detached as well. To prevent this, Weisenfeld recommends visiting your doctor who can trim down or entirely remove the dead nail, which will allow the new nail room to grow in properly.
Another time you should visit your doctor is if the skin surrounding your blackened nail is red, inflamed, or oozing. This may be a sign of an infection, Sutera says, and you should apply an antibiotic ointment until you can get an appointment.
To avoid black toenails caused by repetitive trauma, Jordan Metzl, M.D., a sports medicine physician at the Hospital for Special Surgery in New York City, recommends either trying a bigger shoe or wearing a thinner sock (thick socks may cause too much pressure on your toenails).
Subungual Hematoma
Dropping a heavy object (say, a dumbbell) onto your foot can burst the blood vessels under your nail bed and cause blood to pool underneath, Wiesenfeld explains. This type of black nail—clinically called subungual hematoma—is especially easy to identify, as it will appear almost immediately after an incident.
The build up of blood typically causes a painful throbbing sensation that can be addressed by pricking a tiny needle through the nail to drain out the blood. This procedure will alleviate both the pressure and dark color under the nail—and should always be done by your doctor, Sutera says. At-home attempts are often unsanitary, ineffective, and more excruciating than in-office care.
Most subungual hematomas are purely accidental, so Metzl recommends making foot protection a priority to reduce your risk of getting one in the first place.
The build up of blood typically causes a painful throbbing sensation that can be addressed by pricking a tiny needle through the nail to drain out the blood. This procedure will alleviate both the pressure and dark color under the nail—and should always be done by your doctor, Sutera says. At-home attempts are often unsanitary, ineffective, and more excruciating than in-office care.
Most subungual hematomas are purely accidental, so Metzl recommends making foot protection a priority to reduce your risk of getting one in the first place.
Fungal Infections
Fungal infections—like athlete’s foot—can spread to your toenails and turn them shades of yellow, blue, green, brown, purple, and black, Sutera explains. This range in color is unique to fungus, as is the presence of subungual debris—a chalky white substance that lines the nail bed and often carries a funky odor.
If you think you may have a fungal infection, head to your doctor—he or she can clip and biopsy a portion of your nail to confirm a diagnosis. Treatment options vary depending on the severity of the infection. Mild cases are often addressed with topical medications, while more aggressive fungi require oral medication or even laser treatment.
According to the American Academy of Dermatology, keeping your toenails short, wearing properly-fitted and breathable shoes and socks, not going barefoot in public areas like locker rooms, and not using anyone else’s shoes, socks, nail clippers, or nail files can help prevent a fungal infection in your toenail.
If you think you may have a fungal infection, head to your doctor—he or she can clip and biopsy a portion of your nail to confirm a diagnosis. Treatment options vary depending on the severity of the infection. Mild cases are often addressed with topical medications, while more aggressive fungi require oral medication or even laser treatment.
According to the American Academy of Dermatology, keeping your toenails short, wearing properly-fitted and breathable shoes and socks, not going barefoot in public areas like locker rooms, and not using anyone else’s shoes, socks, nail clippers, or nail files can help prevent a fungal infection in your toenail.
Skin Cancer
Subungual melanoma—the most serious form of skin cancer—can grow underneath your nail bed on the nail plate and cause hyperpigmentation of the skin, Sutera explains. It’s often a slow and painless growth, which makes it especially tricky to catch.
One ominous sign is discoloration that extends beyond the nail and onto the cuticle, Weisenfeld says. “If you’ve had no incidence of trauma, and your nail is slowly starting to change color—especially if that color goes beyond your nail—you should get it checked out by your doctor,” she advises.
Regularly-pedicured patients should do a quick scan of their toes in between polish changes to catch any new developments, Weisenfeld adds. Everyone should ask their doctors to do a yearly skin check.
While melanoma can be deadly, it’s extremely rare and treatable if detected early. Surgery is the only treatment option for subungual melanoma, where the surgeon will remove your entire nail to remove the melanoma growth. Since subungual melanoma isn’t caused by sun, it can be harder to prevent than other forms of cancer. But keeping your feet generally clean and healthy may help.
One ominous sign is discoloration that extends beyond the nail and onto the cuticle, Weisenfeld says. “If you’ve had no incidence of trauma, and your nail is slowly starting to change color—especially if that color goes beyond your nail—you should get it checked out by your doctor,” she advises.
Regularly-pedicured patients should do a quick scan of their toes in between polish changes to catch any new developments, Weisenfeld adds. Everyone should ask their doctors to do a yearly skin check.
While melanoma can be deadly, it’s extremely rare and treatable if detected early. Surgery is the only treatment option for subungual melanoma, where the surgeon will remove your entire nail to remove the melanoma growth. Since subungual melanoma isn’t caused by sun, it can be harder to prevent than other forms of cancer. But keeping your feet generally clean and healthy may help.
Skin Tone
Occasionally, dark discoloration of the nail bed is merely a matter of skin tone. Sutera sees this most often in patients of color. “There’s skin underneath your toenails, and just like skin anywhere else on your body, the pigmentation can change over time,” she explains.
Often, this type of discoloration is symmetrical and seen on multiple toes. For example, both of your pinky toes may develop discoloration of a similar size and shape. Another telltale sign: similar coloring underneath your fingernails. These factors can help distinguish this type of benign black nail from more malignant ones, which are usually contained to just one nail. Even so, Sutera recommends getting any new and usual color changes checked by your podiatrist or dermatologist, just to be safe.
Often, this type of discoloration is symmetrical and seen on multiple toes. For example, both of your pinky toes may develop discoloration of a similar size and shape. Another telltale sign: similar coloring underneath your fingernails. These factors can help distinguish this type of benign black nail from more malignant ones, which are usually contained to just one nail. Even so, Sutera recommends getting any new and usual color changes checked by your podiatrist or dermatologist, just to be safe.
