While most people look for melanoma on their skin, it is a clinical fact that this type of cancer can also develop in the tissue beneath the fingernails and toenails. Known as subungual melanoma, this rare form of the disease does not usually present as a typical mole but rather as a streak or a change in the appearance of the nail itself. Because it is often mistaken for a simple bruise or a fungal infection, understanding the specific visual markers of nail melanoma is essential for ensuring that any suspicious changes are assessed by a medical professional.
What We’ll Discuss in This Article
- Defining what subungual melanoma is and where it originates.
- Common visual signs such as dark streaks or pigment changes.
- Distinguishing between a nail bruise and a potential malignancy.
- Identifying Hutchinsons sign and its significance in diagnosis.
- Why the thumb and big toe are the most frequent sites.
- The importance of professional assessment for persistent nail marks.
- How healthcare specialists evaluate and diagnose nail-based lesions.
Understanding the nature of subungual melanoma
Subungual melanoma is a type of skin cancer that starts in the nail matrix, which is the area where the nail begins to grow. Unlike other forms of melanoma that are heavily linked to ultraviolet radiation from the sun, this specific type is not as strongly associated with sun exposure. It can affect people of all skin tones and is often diagnosed in individuals of African or Asian descent more frequently than other types of melanoma. Because the cancer develops beneath the hard nail plate, it can be difficult to see in its earliest stages, often appearing first as a faint vertical line of pigment.
Identifying the visual signs of a suspicious nail streak
The most common indicator of subungual melanoma is a vertical brown or black streak that runs the length of the nail. This band of pigment typically starts at the base of the nail, near the cuticle, and extends to the free edge. While many people have harmless pigmented streaks in their nails, especially those with darker skin, a streak that is changing is a cause for concern. Signs that a nail streak requires investigation include it becoming wider over time, the borders becoming blurred, or the pigment changing in its intensity or colour.
Distinguishing between a bruise and melanoma
It is very common for people to develop a dark spot under a nail due to a subungual haematoma, which is simply a bruise caused by an injury. A bruise will typically grow out with the nail over several months and will eventually disappear as the damaged area moves toward the tip. In contrast, a subungual melanoma stays in the same position at the base of the nail and continues to produce a pigmented streak even as the nail grows. If a dark mark under your nail does not move or fade over a period of eight to twelve weeks, it should be examined by a healthcare professional to rule out a more serious cause.
Recognising Hutchinsons sign in nail health
Hutchinsons sign is a specific clinical marker that doctors look for when evaluating a suspicious nail. This occurs when the pigment from a nail streak spreads beyond the nail plate and into the surrounding skin of the cuticle or the nail fold. A healthy bruise or a benign pigment streak will be confined strictly to the nail itself. If you notice that the dark colour is appearing on the skin adjacent to the nail, this is considered a significant sign that the pigment cells are behaving abnormally and requires a priority medical assessment.
Common locations and the role of the thumb and big toe
While subungual melanoma can occur on any digit, it is most frequently identified on the thumb or the big toe. These digits have a larger nail matrix and are often subject to more trauma, which sometimes leads to the initial discovery of the lesion. However, any nail on the hands or feet that develops a new or changing pigmented band should be monitored with the same level of scrutiny. It is also possible for the cancer to cause the nail to become brittle, to lift away from the nail bed, or to develop a split that does not heal.
The importance of a professional clinical review
A healthcare professional will use a systematic approach to determine if a nail mark is benign or suspicious. They may use a dermatoscope to look closely at the pigment patterns within the nail streak, looking for irregularities in the spacing and thickness of the lines. Clinical guidelines from NICE state that any unexplained pigmentation of the nail, especially if it is increasing in size or affecting the surrounding skin, should be referred for specialist assessment. If the specialist remains concerned, they may perform a biopsy, which involves removing a small piece of the nail matrix to be checked for cancerous cells under a microscope.
Managing nail health through regular inspection
Regularly checking your fingernails and toenails while they are free of polish or artificial coverings is the best way to catch changes early. Many people do not realise that nail polish can hide the early signs of subungual melanoma for many months. Taking the time to inspect the base of each nail and the condition of the cuticles every few weeks allows you to become familiar with what is normal for you. If you notice a new streak that was not there before, or if an old mark is starting to change, documenting the appearance with a photograph can help your doctor track its progress.
Conclusion
Subungual melanoma is a rare but serious condition that appears as a pigmented streak or patch under a finger or toenail. Differentiating between a common bruise and a malignant growth requires monitoring the mark to see if it grows out with the nail or stays fixed at the base. Recognising Hutchinsons sign and being aware of changes in the thumb and big toe are critical for early detection. If you experience severe, sudden, or worsening symptoms, call 999 immediately.
Can a fungal infection look like melanoma?
Yes, some fungal infections can cause dark discolouration of the nail, but they usually cause the nail to thicken or crumble, whereas melanoma often presents as a distinct streak.
Is subungual melanoma caused by the sun?
Unlike most other skin cancers, subungual melanoma is not strongly linked to UV exposure, though the exact causes are still being researched.
How fast does a nail bruise grow out?
A fingernail usually takes about six months to grow out completely, while a toenail can take up to a year or more.
Does nail melanoma always produce a dark streak?
No, some nail melanomas are amelanotic, meaning they have no pigment and might appear as a persistent sore or a growth that lifts the nail.
Should I be worried about multiple streaks on different nails?
Multiple streaks are more likely to be benign pigment changes, especially in people with darker skin tones, but a single new streak on one nail is more suspicious.
Can an injury to the nail cause melanoma?
There is no evidence that a single injury causes melanoma, but an injury often brings a persons attention to a nail mark that was already present.
What is the first step if I see a streak under my nail?
The first step is to see a general practitioner who can evaluate the mark and decide if a specialist referral is necessary.
Authority Snapshot (E-E-A-T)
This article is designed to provide clear and factual information regarding skin health for the general public. The content is written by the Medical Content Team and has been reviewed by Dr. Stefan Petrov. He is a UK-trained physician with an MBBS and postgraduate certifications including Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), and the UK Medical Licensing Assessment (PLAB 1 & 2). He has hands-on experience in general medicine, surgery, anaesthesia, ophthalmology, and emergency care. Dr. Petrov has worked in both hospital wards and intensive care units, performing diagnostic and therapeutic procedures, and has contributed to medical education by creating patient-focused health content and teaching clinical skills to junior doctors.
