This Specific Fingernail Mark Could Be a Melanoma Symptom

Don't brush off this easy-to-ignore symptom.

When you think of skin cancer, you probably think of checking head to toe for moles. But did you know your nails can also reveal an important sign of melanoma?

Manicurist Jean Skinner had firsthand experience catching this stealthy symptom. “I had a walk-in nail client a couple of weeks ago,” she wrote in an August 2017 Facebook post. “She had a straight dark vertical stripe down her nail. She said as soon as she sat down—I need a color dark enough to cover this stripe.”

Other salons had speculated that the woman’s mysterious line could be due to a calcium deficiency, a blood blister, or a strange hereditary mark. Yet Skinner knew better and was concerned. She immediately told her customer that the dark line was likely a  symptom of melanoma. (Don’t miss these other 15 cancer symptoms women are likely to ignore, either.)

Subungual melanoma (aka nail melanoma) is, as its nickname suggests, is a skin cancer that occurs under the nail. It affects 0.7 to 3.5 percent of people with melanoma, according to the Journal of the American Academy of Dermatology. Though subungual melanoma is an uncommon type of skin cancer, it’s important to know about its telltale sign: a dark black or brown line across a finger or toenail, according to the American Academy of Dermatology (AAD).

close up of a bit toe with a black stripe; nail melanomaCourtesy AIM at Melanoma Foundation

Skinner’s hunch was correct—and unfortunately the prognosis wasn’t good. The client called later to tell her she had aggressive melanoma that had spread to her lymph nodes. (Here are 10 places where you can get skin cancer other than your skin).

A black band isn’t the only skin cancer symptom that could be hiding under your nail polish. Other signs of nail melanoma include darkened skin around the nail and cuticle, blood, pus, and splits in the nail, according to the AAD.

In addition to checking your fingernails for dark marks, you should do your own skin self-exams to check for irregular moles that may indicate melanoma or other types of skin cancer. According to the AAD, one in five Americans will develop skin cancer in their lifetime. See your dermatologist if you see any moles that exhibit any of the ABCDEs of melanoma: asymmetry; irregular borders; varied color including shades of tan, brown, black, white, red, or blue; a diameter of 6mm or more; or evolving size, shape, or color. According to the Skin Cancer Foundation, melanoma is almost always treatable if detected early but if left alone, it can spread to other areas of the body where it can be potentially life-threatening. While melanoma is not the most common type of skin cancer, it causes the most deaths.

As with other skin cancers, early diagnosis of subungual melanoma is crucial, so see your doctor right away if you happen to notice a dark mark under your fingernail or any other suspicious symptoms. Your doctor or dermatologist can do a biopsy to determine if the irregular growth or discolored area is a sign of skin cancer. Now that you’re looking at your own hand, check for these 10 surprising diseases your hands might predict.

Medically reviewed by Joshua Zeichner, MD, on October 29, 2019