Melanonychia
A brown or black band of pigment in the nail
Quick Facts
- Type: Nail pigmentation
- Appearance: Brown or black streak, often vertical
- Most cases: Benign (harmless)
- Key concern: Ruling out melanoma
Overview
Melanonychia is a brown or black discoloration of the nail caused by an increase in melanin, the natural pigment that gives skin and hair their color. It most often appears as a vertical (lengthwise) band running from the base to the tip of the nail, known as longitudinal melanonychia, although it can affect part or all of the nail.
Most cases of melanonychia are harmless. It is common and often normal in people with darker skin tones, and it can be caused by injury, medications, or benign growths of pigment cells. However, in a small number of cases a pigmented nail band can be a sign of melanoma, a serious skin cancer that can occur under the nail. Because of this, new or changing nail pigmentation should be evaluated to make sure it is benign.
Symptoms
The main feature is a brown or black discoloration of the nail. Features that are usually reassuring include:
- Several nails affected with similar bands
- A band that has been stable for a long time
- Even color and regular borders
- Common in people with naturally darker skin
Features that are more concerning and should be checked promptly include:
- A single band that is new, widening, or darkening
- Irregular color or blurred edges
- Pigment spreading onto the surrounding skin around the nail
- Nail changes such as splitting, cracking, or a nodule
- A band appearing in a single nail in an adult
Causes
Melanonychia results from extra pigment in the nail, which can have many causes:
- Increased pigment production: Common and often normal in people with darker skin, sometimes affecting several nails.
- Benign moles in the nail: Harmless clusters of pigment cells under the nail.
- Trauma or friction: Repeated injury, such as from footwear or nail biting.
- Medications and medical conditions: Certain drugs and some systemic conditions can cause nail pigmentation.
- Melanoma: Uncommon but important, a cancerous growth of pigment cells under the nail.
Risk Factors
- Darker skin tones, in which benign melanonychia is common
- Repeated trauma or pressure on the nail
- Use of certain medications
- A history of melanoma or many moles, for melanoma-related cases
Most pigmented nail bands are not dangerous, but a single, new, or changing band, especially in a lighter-skinned adult, deserves evaluation.
Diagnosis
A clinician, often a dermatologist, evaluates the pattern of pigmentation to decide whether it is likely benign or needs further testing:
- Examination and history: Looking at how many nails are involved, the band's color, width, borders, and whether it has changed.
- Dermoscopy: A handheld magnifier to examine the pigment in detail.
- Nail biopsy: Taking a small sample of the nail matrix when melanoma cannot be confidently ruled out; this is the only way to be certain in worrisome cases.
Treatment
Treatment depends entirely on the cause:
- No treatment needed: Benign melanonychia, such as that from darker skin or stable moles, usually requires only reassurance and occasional monitoring.
- Removing the cause: Stopping a responsible medication or addressing ongoing trauma when relevant.
- Monitoring: Periodic checks and photographs for bands that look benign but warrant follow-up.
- Surgery: If a biopsy shows melanoma, prompt surgical treatment is needed, with care guided by a specialist.
The most important step is distinguishing harmless pigmentation from melanoma, since early detection of melanoma greatly improves outcomes.
Prevention
- Most melanonychia cannot be prevented, especially benign pigmentation
- Avoid repeated trauma to the nails, such as from poorly fitting shoes or nail biting
- Check your nails periodically and note any new or changing bands
- Report new or changing nail pigmentation to a clinician for evaluation
When to See a Doctor
See a doctor or dermatologist if you develop a new brown or black nail band, or if an existing band is widening, darkening, has irregular color or borders, spreads onto the surrounding skin, or is accompanied by nail damage or a lump. A single pigmented band that appears in one nail in an adult is especially worth checking, because, although most melanonychia is harmless, prompt evaluation helps catch the rare case of melanoma early.
Frequently Asked Questions
What is melanonychia?
Melanonychia is a brown or black discoloration of the nail caused by extra melanin pigment, usually appearing as a vertical band. Most cases are harmless, but some can be a sign of melanoma, so new or changing bands should be evaluated.
Is a dark line in my nail dangerous?
Most dark nail bands are benign, especially if several nails are affected, the band is stable, and you have darker skin. A single new or changing band, particularly in a lighter-skinned adult, is more concerning and should be checked to rule out melanoma.
What causes a brown or black band in the nail?
Causes include increased pigment production (common and often normal in darker skin), benign moles under the nail, trauma or friction, certain medications, and, less commonly, melanoma. A clinician can help determine the cause.
When should I worry about nail pigmentation?
Be cautious about a band that is new, widening, or darkening, has irregular color or blurred edges, spreads onto the skin around the nail, or comes with nail damage. These warning signs warrant prompt evaluation by a dermatologist.
How is melanonychia diagnosed?
A dermatologist examines the nail, often with a magnifying tool called a dermoscope, and considers how it looks and whether it has changed. If melanoma cannot be ruled out, a small biopsy of the nail is the only way to be certain.
References
- American Academy of Dermatology Association. Nail conditions.
- MedlinePlus, U.S. National Library of Medicine. Nail abnormalities.
- Cleveland Clinic. Melanonychia.
- National Cancer Institute (NCI). Melanoma treatment.