What Causes Black Toenails? Common Reasons and When to Worry
Noticing that one of your toenails has turned black can be unsettling—especially when you do not remember injuring it. Sometimes the explanation is simple, such as pressure from tight shoes or a bruised nail after hitting your toe. Other times, a dark toenail can point to an infection or another condition that deserves medical attention.
So, what causes black toenails? The most common reasons include blood trapped beneath the nail after an injury, repeated pressure from shoes, fungal or bacterial infections, and natural or medication-related pigmentation. Rarely, a dark streak or patch beneath a nail can be a sign of melanoma.
The color alone cannot tell you the cause. Pain, nail thickness, how quickly the color appeared, and whether the dark area moves as the nail grows can provide useful clues.
Quick Answer
Black toenails are most commonly caused by bruising or bleeding under the nail after an injury or repeated pressure from shoes. Fungal infections, bacterial infections, pigmentation, and certain medications can also darken toenails. A new or changing dark streak without an obvious injury should be checked by a dermatologist to rule out more serious causes.
What Does a Black Toenail Actually Mean?
Your toenail itself is a hard plate made mostly of keratin. Beneath it sits the nail bed, which contains sensitive skin and tiny blood vessels.
When blood, pigment, infection, or debris develops underneath or within the nail, the nail can appear brown, purple, dark green, or almost black.
That means a “black toenail” is not one specific condition. It is a visible change that can have several different causes.
The details matter.
Ask yourself:
- Did you recently stub your toe or drop something on it?
- Have you started running, hiking, or wearing different shoes?
- Is the nail painful or throbbing?
- Is it also thick, crumbly, or lifting?
- Is there redness, swelling, drainage, or odor?
- Is the dark area growing outward with the nail?
- Is there a new dark stripe that starts near the cuticle?
These clues can help you decide whether simple monitoring is reasonable or whether it is time to see a professional.
1. Trauma and Blood Under the Toenail
The most common reason for a suddenly dark toenail is an injury.
A hard impact can break tiny blood vessels under the nail. Blood then collects between the nail plate and nail bed, producing a red, purple, brown, or black patch.
This is called a subungual hematoma.
Common causes include:
- Stubbing your toe
- Dropping something heavy on your foot
- Catching the toe under furniture
- Sports injuries
- Accidentally kicking a hard surface
- Pressure from poorly fitting shoes
You may remember exactly when the injury happened. In other cases, especially with mild repetitive pressure, you may not remember a specific accident.
The American Academy of Dermatology explains that nail injuries can occur from sports, accidents, or improperly fitting footwear. Its [guidance for caring for an injured nail] guidance for caring for an injured nail also notes that particularly painful, black, or purple nails may require medical evaluation.
What a Bruised Toenail Usually Looks Like
A trauma-related black toenail commonly has:
- A dark patch underneath the nail
- Tenderness shortly after the injury
- Throbbing when pressure builds under the nail
- Swelling around the toe
- A clear history of impact or repeated pressure
As the nail grows, the dark area should gradually move toward the end of the toe.
Toenails grow slowly, so discoloration can remain visible for many months.
2. Running, Hiking, and Tight Shoes
You do not need one dramatic injury to develop a black toenail.
Repeatedly hitting the front or top of your shoe can create many tiny injuries underneath the nail. Runners sometimes call this “runner’s toe.”
It can also happen during:
- Long walks
- Hiking downhill
- Tennis
- Soccer
- Dancing
- Fitness classes
- Jobs that involve standing or walking for long periods
Shoes that are too short, narrow, or tight around the toes increase friction and pressure.
Even shoes that normally feel comfortable can cause trouble during long workouts because feet may swell during activity.
How to Reduce Repetitive Nail Trauma
Choose footwear with enough space for your toes to move comfortably.
It also helps to:
- Keep toenails neatly trimmed.
- Avoid cutting them extremely short.
- Wear moisture-wicking socks.
- Replace shoes that have lost their shape or cushioning.
- Make sure your toes are not repeatedly striking the front of the shoe.
- Consider professional shoe fitting if black toenails keep returning.
Repeated black toenails should not simply be accepted as normal. Recurring trauma can damage the nail and may make it more likely to lift or become distorted.
3. Toenail Fungus
Fungal nail infection, or onychomycosis, is another possible cause of dark toenail discoloration.
Toenail fungus is more likely when the dark color develops gradually rather than suddenly after an injury.
The American Academy of Dermatology’s [guide to nail fungus symptoms] guide to nail fungus symptoms notes that fungal nails can become yellow, brown, greenish-black, or black. They may also thicken, crack, crumble, or lift from the nail bed.
Look for changes such as:
- Thickening
- Yellow, brown, or black discoloration
- Crumbling edges
- Debris underneath the nail
- Nail lifting
- Distorted shape
- More than one affected toenail
Fungus is especially common in toenails because shoes can create a warm, moist environment.
Risk can also increase when you frequently walk barefoot in shared wet spaces such as locker rooms, pools, or communal showers.
Can You File Away a Dark Fungal Toenail?
No.
A nail file may reduce rough or thick edges, but filing does not eliminate a fungal infection because the fungi can live within the nail and in tissue underneath it.
Aggressively filing a damaged nail can also make it thinner, irritated, or painful.
If you use a nail file on a suspicious toenail:
- Do not share it.
- Consider using a disposable file.
- Wash your hands afterward.
- Avoid using the same file on healthy nails.
- Stop if filing causes pain or bleeding.
A dermatologist can determine whether the problem is actually fungus. Several nail disorders can look similar, so treating every dark nail with an antifungal product can waste time and money.
4. Bacterial Nail Infection
Some bacterial infections can produce dark green or greenish-black discoloration.
The risk is higher when the nail has lifted away from the nail bed, because moisture and microorganisms can collect underneath it.
Warning signs may include:
- Green-black discoloration
- Nail lifting
- Tenderness
- Redness around the nail
- Swelling
- Drainage
- Unpleasant odor
A bacterial infection should not be covered repeatedly with artificial nails or thick layers of polish in an attempt to hide it.
Those products can make it harder to monitor changes and may trap additional moisture.
If the skin around the nail becomes increasingly red, swollen, warm, or painful—or if you see pus—seek medical advice.
5. Natural Nail Pigmentation
Not every dark toenail is a bruise or infection.
Some people naturally develop brown or black pigment within their nails. This type of pigmentation is called melanonychia.
It may appear as a vertical brown or black band.
Pigmented nail bands can occur for several reasons, including normal melanin production, friction, inflammation, medication effects, or other nail conditions. They are also more common in people with darker skin tones.
The difficulty is that a harmless pigmented band can sometimes look similar to a more concerning nail change.
That is why a new, widening, irregular, or changing dark band deserves professional evaluation rather than a DIY diagnosis.
6. Medication-Related Nail Changes
Certain medications can cause nail pigmentation.
The change may appear as brown, black, blue-gray, or other discoloration and can involve one or several nails, depending on the medication.
Medication-related nail pigmentation is uncommon compared with trauma or fungus, but it is worth considering if several nails change after you start a new prescription or medical treatment.
Do not stop a prescribed medication because your nails change color.
Instead, show the change to the healthcare professional who prescribed the medication. They can determine whether the nail change could be an expected side effect or whether another cause needs investigation.
7. Melanoma Under a Toenail
This is the cause people understandably worry about most.
Melanoma can develop underneath or around a nail. It is uncommon, but it is important not to overlook.
The American Academy of Dermatology describes a brown or black vertical line beneath a toenail as one possible sign of melanoma on the foot. Its [guide to signs of melanoma on the foot] guide to signs of melanoma on the foot recommends evaluation by a board-certified dermatologist when a suspicious nail or foot change appears.
Signs that deserve medical attention include:
- A new dark stripe with no known injury
- A stripe that becomes wider
- Uneven or irregular coloration
- Pigment spreading onto the skin beside the nail
- Nail splitting
- Nail lifting without an obvious explanation
- A bump beneath the nail
- Bleeding or a sore that does not heal
A melanoma may not hurt, so lack of pain does not prove that a dark nail is harmless.
At the same time, most black toenails are not melanoma.
The goal is not to panic. It is to have unexplained or changing pigmentation examined instead of trying to diagnose it from photos online.
Black Toenail Causes at a Glance
| Possible cause | Typical clues | DIY care appropriate? | Professional evaluation |
|---|---|---|---|
| Bruise from injury | Sudden dark patch, pain, known trauma | Often, if mild | Needed for severe pain, major injury, or large bruise |
| Repetitive shoe pressure | Running/hiking, toe rubbing shoe, recurring dark nails | Footwear changes may help | Consider if repeatedly returning |
| Nail fungus | Thick, crumbly, discolored or lifting nail | Basic hygiene helps | Useful for diagnosis and treatment |
| Bacterial infection | Green-black color, redness, swelling or drainage | Not ideal for DIY treatment | Recommended |
| Natural pigmentation | Stable brown/black stripe or pigmentation | Monitoring may be appropriate | New or changing bands should be checked |
| Medication effect | Change after starting treatment, sometimes several nails | Do not stop medication yourself | Discuss with prescribing clinician |
| Nail melanoma | New/changing dark stripe, spreading pigment, nail destruction | No | Dermatologist evaluation is important |
How to Care for a Black Toenail After a Minor Injury
If you clearly injured the toe and the damage is mild, basic supportive care may be enough.
1. Reduce Pressure
Switch to roomy shoes or sandals if they can be worn safely.
Avoid exercise that makes the toe hurt.
2. Keep the Area Clean
Wash gently with soap and water.
If skin around the nail is damaged, keep the area clean and protected.
3. Use Cold Therapy for a Recent Injury
A cool pack wrapped in cloth may help with swelling during the early stage of an injury.
Never place ice directly against bare skin.
4. Protect the Nail
If the nail is loose, avoid pulling it off.
A light protective dressing can prevent it from catching on socks or bedding.
5. Watch the Nail Grow
A bruise should gradually travel toward the tip as the toenail grows.
If the dark area remains stationary near the base, changes shape, or becomes larger without another injury, schedule an evaluation.
Expert Tip: Take a clear photo of the toenail today and another every few weeks under similar lighting. Photos make it much easier to tell whether a bruise is growing outward with the nail or whether an unexplained dark area is changing.
Should You Drain a Black Toenail Yourself?
A painful collection of blood beneath a nail sometimes needs drainage.
That does not mean you should burn, drill, pierce, or cut your toenail at home.
Improvised drainage can cause:
- Burns
- Nail-bed damage
- Bleeding
- Infection
- Additional pain
Large, painful hematomas are better evaluated by a healthcare professional, especially after a crushing injury because there may also be damage to the nail bed or bone.
Professional care may cost more than basic home care, but attempting an invasive DIY procedure to save money can create a more complicated injury.
Nail Tools, Hygiene, and Sensitive Toenails
When a toenail is dark, damaged, or possibly infected, be extra careful with nail tools.
Clippers and files should be clean and used gently.
Avoid:
- Digging under the nail with sharp tools
- Aggressively buffing the dark area
- Cutting deep into the corners
- Sharing files or clippers
- Using the same disposable file on infected and healthy nails
People with sensitive skin should also be cautious with acetone, strong antiseptics, nail glue, and other products around irritated skin.
If a nail is painful, inflamed, or possibly infected, cosmetic treatment should come second to figuring out what is causing the problem.
Can You Get a Pedicure With a Black Toenail?
It depends on why the nail is black.
If you simply have an old, painless bruise that is growing out normally, a gentle cosmetic pedicure may eventually be reasonable.
But postpone salon treatment if you have:
- Significant pain
- An open wound
- Bleeding
- Red or swollen skin
- Drainage
- Suspected fungus
- A loose nail
- Unexplained dark pigmentation
A nail technician can help with cosmetic grooming, but they should not be expected to diagnose a medical condition.
If there is doubt about the cause, get the nail checked first.
When to See a Nail Technician or Dermatologist
A nail technician is appropriate for normal cosmetic maintenance of healthy nails.
A dermatologist, podiatrist, urgent-care clinician, or other qualified medical professional is more appropriate when you have symptoms suggesting injury, infection, or an unexplained nail disorder.
Arrange medical evaluation if:
- The nail turns black without an obvious injury.
- You develop a new or changing dark stripe.
- Pigment spreads to the skin around the nail.
- Pain is severe or throbbing.
- Much of the nail becomes dark after an injury.
- The toe is badly swollen or difficult to move.
- The nail is lifting significantly.
- You notice pus or worsening redness.
- You develop fever along with an infected-looking toe.
- The nail becomes progressively thicker or more distorted.
- A suspected fungal infection is not improving.
- You have diabetes, poor circulation, or a weakened immune system and develop a foot or nail problem.
The American Academy of Dermatology also recommends dermatologic evaluation for new or changing dark nail streaks because melanoma can sometimes develop beneath a nail.
How to Prevent Black Toenails
Not every cause is preventable, but good foot and nail habits can reduce common problems.
Wear Properly Fitting Shoes
There should be enough room around the toes without allowing your foot to slide excessively.
This is especially important for runners and hikers.
Trim Toenails Carefully
Cut them reasonably straight across and avoid cutting extremely short.
Do not dig deeply into the corners.
Keep Feet Dry
Change damp socks after exercise.
Allow shoes to dry between uses.
Avoid Sharing Nail Tools
Files, clippers, and other pedicure tools can carry microorganisms.
Clean reusable tools appropriately and replace worn disposable files.
Protect Your Feet
Wear suitable footwear during sports, work, and activities where your toes could be crushed or struck.
Check Your Nails Regularly
Removing polish periodically makes it easier to notice changes in nail color, thickness, and shape.
Common Mistakes to Avoid
- Assuming every black toenail is fungus. Trauma and pigmentation can look similar.
- Treating unexplained dark streaks with antifungal products for months. A new or changing stripe deserves proper evaluation.
- Trying to drill or burn a hole into the nail at home. This can injure the nail bed and introduce infection.
- Aggressively filing a discolored nail. Filing cannot remove fungus living deeper in the nail.
- Pulling off a loose toenail. This may damage sensitive tissue underneath.
- Painting over an infected-looking nail repeatedly. Cosmetic coverage can make changes harder to monitor.
- Sharing nail files or clippers. This can spread fungal or bacterial organisms.
- Ignoring shoe fit. Repeated trauma may continue until the pressure problem is corrected.
FAQs
Can a black toenail be harmless?
Yes. A black toenail commonly develops when blood becomes trapped underneath the nail after an injury or repeated pressure. However, unexplained or changing pigmentation should be evaluated rather than assumed to be harmless.
How long does a black toenail take to grow out?
Toenails grow slowly, so a bruise can remain visible for many months. The important sign is that trauma-related discoloration generally moves toward the end of the toe as new nail grows from the base.
Will a black toenail fall off?
Sometimes. A heavily injured nail may loosen and eventually separate as a new nail grows underneath. Do not pull it off prematurely. Protect the area and seek medical care if there is severe pain, bleeding, swelling, or infection.
Can toenail fungus make a nail black?
Yes. Fungal nail infections can cause brown, greenish-black, or black discoloration, although yellow or white changes are also common. Fungal nails often become thick, brittle, crumbly, misshapen, or lifted as well.
Does a black toenail always hurt?
No. A fresh bruise may be painful or throbbing, but some causes of dark pigmentation cause little or no discomfort. Melanoma beneath a nail can also occur without pain, which is why appearance and changes over time matter.
How can I tell a bruise from melanoma under a toenail?
A bruise usually follows trauma and gradually moves toward the tip as the nail grows. Melanoma may appear as a persistent or changing dark streak or pigmentation that does not behave like a growing-out bruise. You cannot reliably rule melanoma out at home, so suspicious changes should be examined by a dermatologist.
Should I remove nail polish to check a black toenail?
Yes. If possible, remove polish so you can clearly monitor the natural nail. If you notice unexplained pigment, swelling, pain, drainage, nail lifting, or other concerning changes, arrange professional evaluation before covering it again.
Conclusion
So, what causes black toenails? In many cases, the answer is straightforward: a bruised nail from stubbing a toe, running, hiking, or wearing shoes that repeatedly press against the nail.
Fungal and bacterial infections can also darken toenails, while natural pigmentation and medication effects are other possibilities.
The key exception to remember is an unexplained or changing dark streak. Although melanoma beneath a nail is uncommon, it is important enough that suspicious pigmentation should not be ignored.
For a mild, obvious bruise, protect the toe, reduce pressure, keep it clean, and monitor how the discoloration grows out. For persistent, painful, infected-looking, or unexplained black toenails, skip the aggressive DIY fixes and let a dermatologist or other qualified healthcare professional determine the cause.
A few minutes spent checking your toenails regularly can help you spot both everyday nail problems and changes that deserve attention.
