A dark streak under one nail is easy to dismiss as a bruise, especially after a weekend of sport, work or wearing tight shoes. But knowing how to check nail melanoma means looking for change, not trying to diagnose yourself. A suspicious nail change deserves prompt medical assessment. Early action can save your life.
What is nail melanoma?
Nail melanoma, also called subungual melanoma or nail unit melanoma, is a type of melanoma that develops in the skin structures beneath or around a nail. It most often affects the thumbnail or big toenail, but it can occur on any fingernail or toenail.
Unlike many melanomas, nail melanoma may not look like a changing mole. It can appear as a brown, black or grey vertical band, a patch of pigment, a nail that splits or lifts, or a persistent sore around the nail. Some nail melanomas have little or no dark pigment at all.
Nail melanoma is uncommon, but it is serious. It can affect people of every skin tone and may occur on areas not regularly exposed to sunlight. This is one reason it is often missed or mistaken for an injury, fungal infection or ordinary nail damage.
How to check nail melanoma without guessing
A home nail check should take only a few minutes. Once a month, examine all 20 nails in bright natural light or under a clear lamp. Remove nail polish, gel polish and artificial nails first. These products can conceal early changes and make accurate monitoring difficult.
Look at the top of each nail, the skin at the base and sides of the nail, and the skin beneath the nail edge where possible. Compare one hand or foot with the other, but remember that melanoma can affect just one nail. A new or changing mark on a single nail is more concerning than stable, similar pigmentation across several nails.
Take a clear, dated photo if you notice a mark. Include the whole finger or toe in the image so the position and width of a band can be compared over time. Photography can help you describe change to a clinician, but it is not a substitute for an examination.
Warning signs to take seriously
Book a skin check or GP appointment promptly if you notice one or more of the following changes:
- A new brown, black or grey band in one nail, particularly if it is getting wider or darker.
- A band with uneven colour, irregular borders or a blurred appearance.
- Pigment spreading from the nail onto the surrounding cuticle or skin. This can be called Hutchinson’s sign.
- A streak that is wider near the cuticle than at the nail tip, creating a triangular shape.
- Cracking, splitting, distortion, lifting or destruction of a nail without a clear reason.
- A lump, persistent sore, bleeding, crusting or pain around or beneath the nail.
- A red, pink or flesh-coloured growth under the nail that does not heal or keeps returning.
A dark spot from trauma often moves gradually towards the tip of the nail as the nail grows. However, an injury does not rule out melanoma. People may remember bumping a toe or catching a finger after noticing a change that was already there. If the mark does not grow out, changes in shape or colour, or you are uncertain, have it checked.
The ABCDEF guide for nail changes
Clinicians may use the ABCDEF guide as one way to assess pigmented nail bands. It is not a home diagnostic test, but it can help you recognise why a review is needed.
A is for age and ancestry. Nail melanoma is more often diagnosed in adults aged 50 to 70, but younger adults can be affected. It also occurs in people of all backgrounds and skin colours.
B is for band. A brown or black band that is broader than about 3 millimetres, irregular, or becoming wider deserves attention.
C is for change. Look for changes in width, colour, shape or symptoms. A stable mark is generally less concerning than one that evolves, but stability alone cannot confirm that it is harmless.
D is for digit. The thumb, big toe and index finger are more commonly affected, although melanoma can develop in any nail.
E is for extension. Pigment extending onto the nearby skin, cuticle or nail fold is a warning sign.
F is for family or personal history. A previous melanoma, a strong family history of melanoma or numerous atypical moles can increase the reason to seek expert assessment quickly.
The guide has limits. A person can have nail melanoma without matching every point, and many harmless nail changes can match one or two. The key issue is a new, unexplained or evolving change, particularly on one nail.
When a dark nail band may be harmless
Not every pigmented nail band is melanoma. Some people naturally have harmless longitudinal pigmentation, known as melanonychia. It may affect more than one nail, remain consistent over time and be more common in people with darker skin. Certain medicines, inflammatory skin conditions and repeated friction can also alter nail colour.
Fungal infections can cause yellowing, thickening and crumbling. Bruising can cause black or purple discolouration after trauma. Yet these explanations should not be assumed when a nail change is new, unusual or persistent. It is possible to have an injury or infection and a separate suspicious lesion at the same time.
Do not rely on a nail salon, online image search or a friend’s opinion to rule out melanoma. A salon professional may be the first person to spot a change, but a trained clinician must assess it.
What happens at a clinical nail check?
A GP, skin cancer doctor or dermatologist will ask when the change began, whether it has evolved and whether there was an injury. They will examine the entire nail unit and surrounding skin, often using a dermatoscope, a handheld magnifying device with specialised lighting.
Depending on the appearance, the clinician may photograph and monitor the nail over a defined period, arrange specialist review, or recommend a biopsy. A biopsy involves taking a small sample from the relevant nail structure so it can be examined under a microscope. It is the only way to confirm or exclude melanoma when clinical concern remains.
It can be confronting to hear that a biopsy is needed, particularly because nail procedures require care to protect the nail. But delayed diagnosis carries a far greater risk. If melanoma is found early, treatment is usually more straightforward and outcomes are better.
Who should be especially alert?
Everyone should include their nails in routine skin checks. Be particularly vigilant if you have had melanoma or another skin cancer before, have a close family history of melanoma, work outdoors, spend significant time in high-UV conditions, or have many changing pigmented spots.
People with skin of colour should not be overlooked. Melanoma can develop on the palms, soles and nail units, where it may be noticed later. A darker skin tone does not protect against every form of melanoma, and it should never delay a check of a concerning nail change.
Age is also not a reason to wait. While nail melanoma is more frequent in older adults, any persistent, changing or unexplained nail lesion should be assessed regardless of age.
When to book an appointment
Arrange a prompt appointment with your GP, a skin cancer clinic or a dermatologist if a suspicious mark is new, changing, widening or affecting one nail. Aim to be assessed within days rather than waiting for your next routine skin check. Tell the receptionist that you have a changing pigmented nail lesion so the reason for your appointment is clear.
Seek more urgent medical advice if there is significant bleeding, a rapidly growing mass, severe pain, or a non-healing sore around the nail. These symptoms do not always mean melanoma, but they should not be managed by watchful waiting alone.
While you wait for assessment, avoid covering the nail with polish or artificial nails. Keep your dated photographs, note when you first saw the change, and mention any past melanoma or family history. Small details can help your clinician make the right next decision.
Your nails are part of your skin. If one of them is sending a new or changing signal, listen to it and arrange a professional check without delay.