melanoma warning signs

A black toenail is usually a subungual haematoma: blood trapped under the nail after a knock, or after your toe has hit the front of your shoe again and again on a long run. Less often it’s a fungal nail infection, and only rarely is it a subungual melanoma, a skin cancer that grows under the nail.

The most useful clue is how the mark changes over time, because a bruise grows out with the nail and clear nail appears at the cuticle within a few weeks. A dark streak that stays joined to the cuticle, or a mark you can’t link to any knock or long run, needs a prompt check with your GP or podiatrist.

In This Article

• Why toenails turn black: How a single knock, or thousands of small taps inside your running shoe, leaves blood pooled under the nail.
• Bruise or melanoma: A simple four-week grow-out check, plus the warning signs that mean you should see your GP rather than wait.
• What to do and how long it takes: When draining the blood helps, why most bruises are left alone, and how slowly a big toenail grows out.
• Stopping it happening again: Shoe room, lacing and nail care, plus what a study found happens to runners’ feet over a 10 km run.
• Common questions answered: Running with a black toenail, nail polish, a loosening nail, regrowth and whether you need a GP referral.

Why Has My Toenail Turned Black?

How runner’s toe happens

From a shoe that runs out of room to a black toenail

1

The shoe runs out of room

The shoe is a little short, or the foot slides forward, most often downhill or late in a long run.

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2

The toe taps the front of the shoe

The longest toe, often the big toe, takes a small knock with every stride.

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3

Blood collects under the nail

Tiny bleeds pool beneath the nail plate. This is a subungual haematoma, a bruise under the nail.

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4

The nail darkens, often days later

It may not hurt much, which is why many runners can’t remember a single moment it happened.

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5

Where to make changes

Steps 1 and 2 are the ones you can change: room at the front of the shoe, lacing that stops the slide, and short toenails.

If you’ve spotted a dark toenail after a long run on the Main Yarra Trail or a stubbed toe at home, the cause is often blood trapped under the nail. A fungal nail infection, some medicines and a few less common conditions can also darken a nail.

Working out which one fits your situation helps you decide whether to watch it grow out or have it checked sooner.

Bleeding Under the Nail From a Knock or a Long Run

When a toenail turns black after a long run, new shoes or a stubbed toe, the usual cause is blood trapped beneath the nail plate. We call this a subungual haematoma, which simply means a bruise under the nail.

A single knock can do it, but in runners it more often builds up as the toe strikes the front of the shoe over and over, especially downhill or in shoes that are tight or ill-fitting. That’s why it’s often called runner’s toe, and why many people can’t recall a specific injury at all.

A black toenail from a sudden knock often feels painful and throbbing at first, then settles over the following days.

If yours is fresh and throbbing, please don’t pierce it yourself; book online or call Bellevue Podiatry on (03) 9457 2336 so we can assess it and, where appropriate, relieve the pressure.

Fungal Nail Infection

Most black toenails are bruises, but a fungal nail infection (onychomycosis) can also change the nail’s colour. It’s usually yellow, white or brown, though debris under the nail can look darker, which is why black toenail fungus is sometimes mistaken for a bruise.

Feature	Bruise	Fungal Nail
Onset	Often sudden, after a knock or a run	Gradual, over months
Nail texture	Usually smooth	Often thickened and crumbly

Repeated rubbing from footwear can look very similar, so a lab test is recommended to confirm a fungal infection before tablet treatment starts. If you’re wondering how to get rid of black toenails caused by fungus, patience matters, because treatment takes months while healthy nail grows through.

A podiatrist can assess the nail, reduce nail thickness and talk you through toenail fungus treatment options suited to your situation.

This is general information and not a substitute for an individual assessment.

Medicines, Health Conditions and Other Less Common Causes

Not every black toenail is caused by trauma or a fungal infection. In clinic, we also consider medications, underlying health conditions and, rarely, changes that need closer medical review.

Medications

Blood thinners (anticoagulants) raise the risk of bleeding and bruising, so even a minor knock can leave a bigger bleed beneath the nail, forming a subungual haematoma. Some other medicines, including certain chemotherapy drugs, can cause brown or black bands in the nail.

Black Toenail and Diabetes

With diabetes, the main concern with a black toenail is that peripheral neuropathy (reduced sensation) can mean you don’t notice a minor injury, while poor circulation can slow healing.

If you have diabetes and notice nail darkening, see a podiatrist promptly rather than waiting, and ask about a diabetic foot assessment.

Black Toenail Melanoma

Black toenail melanoma (subungual melanoma) is rare, and unlike melanoma on sun-exposed skin, sun exposure doesn’t appear to be a risk factor. Please see your GP if there’s no clear cause for the discolouration, or if you notice:

& A dark streak beginning at the cuticle

& A streak that widens or darkens over time

& Pigment spreading onto the surrounding skin

& Discolouration that doesn’t grow forward with the nail

Will My Black Toenail Fall Off?

Sometimes the nail lifts away from the nail bed and loosens, but often the discoloured section simply grows out with the nail over several months. There’s more on caring for a loose nail in the questions below.

Bruise or Melanoma? How to Tell the Difference

The four-week grow-out check

Is the mark behaving like a bruise?

Week 0

Photograph the toe from directly above in daylight, with a ruler or coin beside it. Note the date.

Weeks 1 to 3

Repeat once a week: same light, same angle, same ruler.

Week 4

Compare the first and last photos, looking at the end of the mark nearest the cuticle.

Clear nail opening up at the cuticle

This is how a bruise behaves. Keep the nail trimmed, and look at your shoe fit and lacing.

See your GP promptly if:

• There’s still no clear nail at the cuticle after four weeks
• A streak runs right back to the cuticle
• The band is about 3 mm or wider, or widening or darkening
• Colour spreads onto the skin around the nail

Can’t link the mark to a knock or a lot of running? Skip the four weeks and see your GP now.

For most people, the clearest clue is time.

A bruise is carried forward as the nail grows and leaves clear nail behind it, while a streak that needs checking stays joined to the cuticle, even as it gets longer.

Because toenails grow only about 1.6 mm a month, four weeks is long enough to see a thin strip of new nail but not much more. That’s why we suggest a weekly photo with a ruler beside the toe, taken in the same light, rather than trusting your memory.

Signs of a Toenail Bruise

A bruise under the nail, known as a subungual haematoma, usually follows a knock, a long downhill run or shoes that are too short. It’s typically reddish-purple to black and may throb in the first day or two.

As the nail plate grows, it carries the discolouration towards the tip of the toe.

Within a few weeks, you’d usually expect to see clear, healthy nail emerging at the cuticle.

Signs That May Point to Subungual Melanoma

Subungual melanoma is a rare form of skin cancer that develops beneath the nail, and it behaves differently from a bruise. Please see your GP promptly if there’s no likely cause for the mark, or if you notice a dark streak that:

& starts at the cuticle

& widens over time

& darkens in colour

& spreads onto the surrounding skin

& doesn’t move forward as the nail grows

Doctors weigh these features together, and a band 3 mm or wider, or colour spreading onto the skin fold around the nail (Hutchinson’s sign), raises more concern. A recent knock doesn’t rule melanoma out, because small knocks are common and easy to blame.

If you’re unsure what you’re looking at, book online or call Bellevue Podiatry on (03) 9457 2336, and we can assess the nail and refer you on if needed.

What to Do About a Black Toenail, and How Long It Takes to Grow Out

Treating a Black Toenail

In most cases, a black toenail caused by a bruise (a subungual haematoma) doesn’t need much treatment.

If the injury is fresh and throbbing, a clinician may release the trapped blood through a tiny hole in the nail, which is supported within 48 hours of injury. Once the tenderness settles, or if it was never sore, it’s usually left to grow out.

Please never attempt this at home, as it carries a real risk of infection and further damage to the nail bed.

How Long Does a Black Toenail Take to Grow Out?

Toenails grow about 1.6 mm a month, so clear, healthy nail often appears at the cuticle within a few weeks. The darkened section then moves gradually towards the tip as the nail grows.

At that rate, a bruised nail on your big toe may take several months, and sometimes over a year, to clear completely.

This slower timeframe is normal and doesn’t usually point to a problem with healing.

When to See a Podiatrist

Please see a podiatrist or your GP promptly if any of the following apply:

& You have diabetes

& You have poor circulation

& You have numb feet or reduced sensation

& You take blood thinners

& The discolouration appeared without any injury you can recall

A mark with no injury behind it needs assessment rather than drainage, because releasing the blood offers no benefit when the bleed wasn’t caused by trauma. To find out what’s behind a black toenail, from poor shoe fit to something that needs a closer look, book online or call Bellevue Podiatry on (03) 9457 2336.

How to Lower the Chance of Another Black Toenail

Most black toenails develop when the toe repeatedly strikes the front of the shoe, so small changes to your footwear and running habits can often lower the risk. Fit changes during a run, too: in a small study of 10 recreational runners, the arch had flattened by the end of a 10 km run, and the gap in front of the big toe closed by about a centimetre within each stride.

So a shoe that feels roomy in the shop can run short late in a long run. In clinic, we generally suggest these practical steps:

• Check shoe fit late in the day: Feet are at their largest by the end of the day, so this gives a truer sense of fit.
• Allow enough toe room: The Australian Podiatry Association suggests around 1.5 cm of space beyond your longest toe, which isn’t always your big toe.
• Lace to stop the slide: The authors of that 10 km study advise lacing firmly enough to stop the foot sliding forward, and a heel lock through the extra top eyelet is one common way to do it on downhill stretches of trails like the Main Yarra or Plenty River.
• Maintain nail care: Keep your toenails trimmed straight across and not too long.

If you’ve had repeated black toenails, a podiatrist can assess your shoe fit, lacing and gait to find the underlying cause, which is a core part of a sports podiatry assessment.

Frequently Asked Questions

Can I Keep Running While I Have a Black Toenail?

In many cases, yes, you can keep running if the affected toe isn’t particularly painful. Fix whatever caused the black toenail first, though, or the same spot will keep taking knocks.

Reducing Pressure on the Nail

Simple footwear changes can protect the injured nail and help prevent a repeat.

• Check your shoe length: Make sure you still have about 1.5 cm in front of your longest toe.
• Adjust your lacing: A heel-lock lace pattern can help stop your foot sliding forward on downhill sections.
• Trim your nails: Keep them straight across and not too long, so the nail edge isn’t the first thing to hit the toe box.

When to Ease Off

If the toe is throbbing or the pressure under the nail is painful, reduce your running and see a clinician within about 48 hours. Within this window, drainage of the trapped blood is often possible and can relieve pressure quickly.

Seek prompt assessment if you notice increasing redness, swelling, warmth or discharge around the nail, as these may point to infection.

Who Should Seek Care Promptly

If you have diabetes, reduced sensation in your feet or take blood thinners, please see a podiatrist promptly rather than waiting. These factors can raise the risk of complications and let a minor injury go unnoticed.

Any dark discolouration that appears without a known injury, or that stays joined to the cuticle instead of growing out, should be checked by your GP.

Book an Appointment

Book online or call Bellevue Podiatry on (03) 9457 2336 to arrange an assessment with one of our podiatrists.

Will My Black Toenail Fall Off, and What Should I Do if It Does?

It may. When blood collects beneath the nail (a subungual haematoma), the pressure can separate the nail plate from the nail bed, and the nail may gradually lift as new nail grows behind it, although many bruised nails stay attached.

If your nail loosens, avoid pulling it off, as this can expose the sensitive nail bed and raise the risk of infection; instead, follow these steps while the new nail grows through:

• Keep the toe clean and dry, washing it gently each day.
• Cover it with a light, breathable dressing.
• Wear roomy, well-fitted shoes to reduce pressure on the toe.
• Carefully trim any loose edges with clean clippers to prevent snagging.

If you have diabetes, reduced sensation in your feet, or signs of infection such as increasing redness, swelling, warmth or pus, book online or call Bellevue Podiatry on (03) 9457 2336. General information like this can’t replace an individual assessment.

Is It Okay to Wear Nail Polish Over a Black Toenail?

Wearing nail polish over a black toenail is generally fine for a special occasion, but it hides the nail plate and stops you seeing how the discolouration changes. With a typical subungual haematoma, we expect the dark area to grow out over several months, so being able to see it is clinically useful.

Polish can also hide warning signs, such as a dark streak that begins at the cuticle and widens over time, which needs prompt professional assessment.

Ideally, leave the nail bare and check it regularly until the discolouration has fully grown out.

Will My New Toenail Grow Back Normally After a Black Toenail?

In most cases, yes. When a damaged nail lifts or falls off, a new nail usually regrows from the nail matrix at the base of the toe, provided the matrix itself wasn’t badly injured.

Regrowth is slow, and a big toenail can take 12 to 18 months to grow back fully. Some people find the new nail grows back thicker, ridged or slightly misshapen, particularly after severe or repeated knocks.

If you’re concerned about how your nail is regrowing, or you have diabetes or poor circulation, book online or call Bellevue Podiatry on (03) 9457 2336.

Do I Need a GP Referral to See a Podiatrist at Bellevue Podiatry?

No, you don’t need a GP referral to see a podiatrist at Bellevue Podiatry. You can book directly online or call our clinic on (03) 9457 2336.

If you live with a chronic condition such as diabetes, your GP may be able to set up a GP chronic condition management plan, which can make up to five allied health visits each calendar year eligible for a Medicare rebate. Private health extras cover may also contribute, so it’s worth checking your level of cover with your fund before your visit.

Conclusion

A black toenail can look alarming, but in most cases it’s simply a bruise that grows out as your nail renews itself. Watch for a dark streak that stays joined to the cuticle, widens, darkens or spreads onto the surrounding skin, and seek prompt care if you have severe pain, diabetes or take blood thinners.

At Bellevue Podiatry, we help people from Rosanna, Heidelberg, Watsonia, Ivanhoe and surrounding suburbs tell a harmless knock from a fungal infection or something that needs a closer look. Book online or call (03) 9457 2336 to have your nail and shoes checked, with your long-term foot health in mind.