A simple stripe or a red flag?

By Heidi Splete, Contributing Writer, November 1, 2025

Lines or streaks on the nails are not uncommon, but deducing the cause of these discolorations is essential for separating benign melanonychia from nail unit melanoma (NUM).

Melanonychia, a brown or black discoloration of the nail, could result from either melanocyte activation or a melanocytic proliferation. Melanocyte activation stems from an increased synthesis of melanin, but with a normal number of melanocytes. By contrast, melanocytic hyperplasia involves not only an increased synthesis of melanin but also increased number of melanocytes.

The difference matters. Melanonychia from melanocytic activation is benign, with wide-ranging causes that include pregnancy, nail trauma, or simply having darker skin. In addition, fungal infections, inflammatory dermatoses, such as psoriasis, and medications, notably some types of chemotherapy, may cause melanonychia.

However, if melanocytic hyperplasia is to blame for a patient’s melanonychia, ruling out NUM is a priority, according to experts

Push for complete history

“The initial evaluation of a patient presenting with melanonychia involves gathering a careful history, including when the band first appeared, associated symptoms including bleeding and pain, family history of melanoma, and a careful medication history,” said Shari Lipner MD, PhD, FAAD, associate professor of clinical dermatology and director of the nail unit at Weill Cornell Medicine in New York.

In terms of clinical evaluation, it is important to record the digit involved and whether other nails are involved, said Dr. Lipner, who was the corresponding author on a review of melanonychia published in the July issue of JAAD.

“I measure the length of the band, both proximally and distally, as well as the width of the entire nail unit, and I look for pigment that may be involving the nail folds,” Dr. Lipner said. She also performs a dermoscopic examination to assess whether the bands are regular or irregular.

Distinguishing benign melanonychia from potential subungual melanoma is a challenge, Dr. Lipner said. “While there are clues to help distinguish benign melanonychia from subungual melanoma, including color of the band, width of the band, band width percentage, and whether there is involvement of the skin of the nail folds, there is no single clinical feature that can determine whether it is benign or malignant,” she said. A nail biopsy is necessary to help make the diagnosis if there is any reason to suspect malignancy, she added.

“Some red flags that would prompt me to do a nail biopsy would be width greater than 3mm, a band width percentage greater than 40%, involvement of the thumb or great toe, recent change, involvement of the nail folds, bleeding, or pain,” said Dr. Lipner.

Research gaps

NUMs are exceedingly rare overall, and studies on this topic are lacking, said Dr. Lipner. “What we really need is an international effort in terms of collecting clinical photos, dermoscopic images, and histopathology to help inform patient care,” she said.

In the review article, Dr. Lipner and colleagues examined the latest research on the evaluation and diagnosis of melanonychia.

Although a nail matrix tangential shave remains the gold standard for confirming or excluding melanoma of the nail, the researchers noted that both onychoscopy and histopathologic examination of nail clippings may be useful triage tools to rule out the need for a biopsy, or to help in biopsy planning, Dr. Lipner and colleagues noted in their review.

Melanoma: Real or not real?

Melanocytic hyperplasia’s noncancerous and common causes include nevi and lentigo. NUM is extremely rare in children, and almost half of pediatric cases of melanonychia are caused by nail matrix nevi, according to Dr. Lipner. However, the potential for cancer is there, and diagnostic criteria are needed to help navigate melanonychia’s gray areas.

The ABCDE criteria for detecting melanoma — most useful for adult patients (J Am Acad Dermatol. 2013 Jun;68(6):913-25) — were developed by dermatologists and are explained by the AAD. The letter ‘F’ for ‘family history’ has been added for nails.

A variation of these criteria applies to assessment of nails, and the definitions are more complicated, wrote Jade Conway, MD, now of Reveal Research Institute in Dallas, and colleagues, in a study published in Cells, on which Dr. Lipner also served as corresponding author.

The criteria are as follows:

Age and ancestry. Age 50-70 years is the most common range for development of subungual melanoma, and data published in a previous study in JAAD support an increased risk among individuals with darker skin.

Bands or borders. Brownish-black bands wider than 3mm or irregular borders are potential signs of NUM, especially in adults (less so in children, see below).

Change in appearance. A change in the appearance of the band or border discoloration, as with skin nevi, should prompt suspicion.

Digital involvement. The three digits most often involved in NUM are the thumb, great toe, and index finger.

Extension. Be suspicious in cases of melanonychia when the pigment extends to the nail fold, also known as Hutchinson’s sign.

Family history. A personal or family history of melanoma or unusual moles has been associated with increased NUM risk.

Diligent dermoscopy

Several distinguishing dermoscopy features can help rule NUM in or out. Parallel lines are often a signature of subungual nevi, while irregular lines may point to subungual melanoma. Other dermoscopy flags for further investigation include a brownish background on the nail and a micro version of Hutchinson’s sign, the extension of color onto the cuticle or surrounding nail tissue that might be too small to see on clinical examination.

Nailing the pediatric diagnosis

Children are not just little adults, especially as it relates to the skin and the nails. There are different considerations when evaluating nail pigment in children. NUM is very rare in children, but melanonychia is not, according to Kelly M. Cordoro, MD, FAAD, a professor of dermatology and pediatrics at the University of California, San Francisco (J Am Acad Dermatol. 2013 Jun;68(6):913-25).

In children, benign cases of melanonychia are very common, but generate an outsized amount of worry and confusion. A brown stripe in a nail is “melanoma until proven otherwise” according to information caregivers read online, but this is nearly all adult data, wrote Dr. Cordoro, corresponding author on a detailed review of pediatric melanonychia with colleagues Mary E. Lohman, MD, FAAD, of the Mayo Clinic, and Timothy H. McCalmont, MD, of the University of California, San Francisco.

As in adults, the causes of melanonychia in children are varied, but data show that more than half of pediatric cases of melanonychia are caused by nevi, in contrast to 12% of adult cases. Similarly, lentigo has been shown to account for approximately 30-70% of pediatric cases, versus 9% of adult cases. “Activation of otherwise quiescent nailbed melanocytes, leading to striped or diffuse melanonychia, is another common cause in children, often due to repetitive trauma from sports and other activities. Medications as well as inflammatory and autoimmune diseases account for a small proportion of melanonychia in children. It is essential to obtain a thorough medical, family, and social history in this age group,” said Dr. Cordoro.

Features of benign melanonychia in children often resemble NUM in adults — wider bands, Hutchinson’s sign, and nail dystrophy are not uncommon, and dermoscopy findings may show seemingly atypical features. However, “the width and spacing of bands do not indicate melanoma in kids,” the authors said. The 3mm band width used as a red flag in adults is unlikely to be helpful in children, and some studies suggest an older age of onset as a diagnostic guide for nail matrix melanoma triage, they added.

When a nail matrix biopsy is pursued in children, which is an intricate and technically challenging procedure, it is critical to have the specimen reviewed by dermatopathologists with expertise in pediatric pigmented lesions. Over- or misdiagnosis of benign melanonychia can lead to unnecessary surgery and aggressive treatments that are reserved for true nail matrix melanoma, Dr. Cordoro added. “Pediatric dermatologists are a very collaborative group, and achieving consensus on the need to biopsy is important. When confronted with a challenging pigmented lesion in a child, I recommend ‘phoning a friend’ to benefit from the collective experience and expertise of board-certified pediatric dermatologists with interest in nail conditions.”

Melanonychia and melanoma management

If melanoma is ruled out, no treatment of melanonychia is necessary in most cases. However, melanonychia caused by an underlying infection or systemic condition may resolve if these conditions are treated.

NUM requires complete excision of the tumor which can usually be accomplished by removing the entire nail unit. For early melanomas, amputation should be avoided. Amputation of the digit may be required for more advanced melanomas. Outcomes have historically been poor because of delayed diagnosis, according to a report published in StatPearls and updated in August 2025.

Early detection makes a substantial difference, according to the article, which cites data from the American Cancer Society showing a five-year survival rate of 97% for subungual melanoma if detected at Stage IA, compared to 15-20% for patients diagnosed at Stage IV. Interest is rising in function-preserving surgeries as an alternative, although data in support of surgical excision versus amputation are limited, according to the article.

Management of melanonychia requires a thorough assessment and starts with history, said Kendall Billick, MD, DTM&H, FRCPC, FAAD, a clinician teacher and nail specialist at the University of Toronto, Canada. “I note their age (pediatric versus adult), ask how long the band has been present, and whether they have noticed any change with time. I also note skin tone and whether multiple nails are involved,” said Dr. Billick, who established a medical and surgical nail clinic at Toronto Western Hospital.

“An important step is to determine if the band is actually melanin as opposed to exogeneous pigment, such as nicotine or nail polish, or endogenous, such as blood, or pigment from bacteria or fungi,” he said.

If Dr. Billick suspects that the band is composed of melanin, his strategy is to examine — clinically and dermoscopically — the band color, width, homogeneity, and any spread onto neighboring skin. For width, he measures both proximally and distally and assesses the percentage of the nail plate that is involved. “I note which digit is affected, and I will sometimes examine the lips and genitals for pigment,” he added.

“The central reason we care so much about longitudinal melanonychia (LM) is in distinguishing benign causes from NUM,” Dr. Billick said. Longitudinal melanonychia is the most common presentation of NUM, but NUM is rare, so most LM bands are benign, he noted. Overall, NUM accounts for just under 4% of all cutaneous melanomas, but it is impossible to know whether the patient in front of you actually has melanoma or not, he said.

Dr. Billick highlighted three key challenges in assessing melanonychia:

Skin tone. “The darker one’s skin tone, the more bands of LM they may have,” Dr. Billick said. The number of NUM is thought to be similar across skin tones, so finding the NUM is harder in patients with multiple bands, he added.

Cutoff for children. “We don’t know at what age children should be treated as adults,” Dr. Billick said. Worrisome findings suggesting NUM in adults are almost always benign in children, but an appropriate age cutoff for concern remains unclear, he said.

Biopsy know-how. “Taking a proper biopsy to assess NUM is challenging in the nail and not taught consistently in residency,” Dr. Billick said. However, biopsy is often the only way to distinguish between benign and malignant causes of LM, he noted.

Although NUM often has no distinguishing features, important clues to potential NUM in an adult include a band involving one finger, a band that is changing with time, a band that takes up more than 40% of the nail plate, and clinical/dermoscopic features of “chaos,” as opposed to homogeneity, he said.

Dr. Billick advises physicians to get into the habit of examining all nails of patients from teens and older. “Maybe even start asking patients to come to appointments without nail polish or artificial nails,” he said. Dr. Billick also recommended that physicians attend conferences to learn nail biopsy techniques themselves or to become better informed and prepared to refer to someone who is skilled in this area. Also, consider photography to monitor nail changes over time; “photography is invaluable,” he emphasized.

As for additional research, markers that would allow a non-invasive diagnosis, or at least help triage, would be very helpful, Dr. Billick said. “Recent publications have examined the use of simple nail clippings, which shows promise, but does not replace biopsy,” he noted.

From examination to collaboration

When seeing a patient with melanonychia for an initial examination, the first question to ask is whether more than one nail is affected, said Adam Rubin, MD, FAAD, a dermatologist, dermatopathologist, and nail expert at NYU Langone Health. Melanonychia involving more than one nail is more likely to have a systemic cause; however, a tumor is more likely when only one nail is affected, he said.

Age is a key factor in guiding clinical assessment of melanonychia, Dr. Rubin said. NUM becomes much more likely with advancing age, and it is extremely unlikely in children, he added.

Patients are more aware of their health in general, and of skin changes in particular, than in the past, and individuals with melanonychia are less likely to present with advanced changes, Dr. Rubin said. Therefore, ask questions about when the patient first noticed the discoloration, and whether it has remained stable, he said. A history of change is an important risk factor for NUM, as is location on the thumb or great toe, Dr. Rubin added.

“Statistically in our laboratory, most nail unit biopsies are benign,” Dr. Rubin said. However, a biopsy remains the only way to definitively diagnose NUM, he added.

Even in cases of benign findings, melanonychia should be recorded and become part of a patient’s medical record, to be reviewed as part of an annual skin exam, and a patient’s self-skin exam, said Dr. Rubin. If a patient with melanonychia reports changes in a band of melanonychia affecting a single nail, it should then be biopsied.

Some cases of melanonychia will likely resolve once their root causes are addressed, Dr. Rubin said. For example, a case of melanonychia caused by a fungal infection should resolve once the fungal infection is cured, but don’t be complacent, he added. Fungal infections can be concurrent with nail tumors, and if the melanonychia doesn’t resolve when the fungal infection has been treated appropriately, further investigation is needed.

Looking ahead, improved diagnostics and treatments involving artificial intelligence may be able to guide melanonychia management, but no specific strategies have been integrated into routine clinical practice at this time, Dr. Rubin said.

Expanded use of nail clippings, however, have shown potential in melanonychia management by serving as a triage before a biopsy, said Dr. Rubin, who was the senior author on an article advocating for the diagnostic value of nail clippings. In the article, published in the Journal of Cutaneous Pathology in 2022, Dr. Rubin and colleagues wrote that melanocyte remnants (melanocyte residues, MR) identified in the nail plate may indicate NUM. Increased number and increased density of them are most concerning, he said.

In cases of melanonychia, whether assessing nail clippings or a soft tissue nail unit biopsy, collaboration with an experienced dermatopathology laboratory team is essential for an accurate assessment and correct diagnosis, said Dr. Rubin. Be sure to use a lab that is familiar with processing nail specimens, he emphasized.

“Nail clipping for melanonychia has the benefits of identifying a potentially benign diagnosis, the helpful information obtained for surgical planning if needed, and the possibility of identifying melanocyte remnants, resulting in rapid triage for nail unit biopsy. This outweighs the potential financial costs and certainly would be preferred by patients instead of direct progression to a soft tissue nail unit biopsy,” Dr. Rubin and colleagues concluded in their article.

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