A doctor explains the differences between a melanoma black line under the fingernail and a normal one.

“Splinters or dark streaks under nails can occur when microscopic areas of bleeding happen and allow blood to settle under the nail,” says Dr. Joel Schlessinger, MD, board certified dermatologist and cosmetic surgeon with a private practice in Omaha, NE.

“This also occurs in psoriasis where nail deformities are common,” he continues.

“A dark streak or area of the nail with dark discoloration can be a sign of melanoma and should be evaluated if there is no reason that trauma could have caused it.

“The dark streak from melanoma is due to actual cells being grown in the nail area or under the nail.”

What’s going on when the cause is benign?

“If the cause of nail streaks is benign it is usually from trauma or psoriasis or simple heredity,” says Dr. Schlessinger.

“Many individuals with skin of color have longitudinal nail streaking or dark streaks over the nails, and sometimes it is difficult to determine if they are benign or not.”

How are melanoma streaks in the nails different in appearance from benign streaks?

Dr. Schlessinger explains, “Hutchinson’s sign in melanoma is the presence of a dark streak along with color changes to the skin just before the nail starts.”







Hutchinson’s sign can also appear in the skin at the top of the nail.

Hutchinson's near the top nail edge

Hutchinson’s near the top nail edge

“This is a very concerning sign and usually is best addressed by a biopsy of the nail bed or, at the very least, evaluation by a dermatologist.”

Melanoma lines under the nails tend to be thicker than the harmless splinter-like lines that many people get.

They also tend to be comprised of varying shades of brown to black, or if just brown, the shades usually still vary.

Melanoma streaks may also be tan, grey or dull pink.

Melanoma streaks may be thick enough to look more like bands than lines.

More Differences

Cancer will also progress, whereas the normal thinner streak that was never there before will eventually disappear.

The harmless subungual hemorrhage (old blood) will be pushed upward over time from new nail growth.

Melanoma will never push upward, but will expand in width.

A malignant tumor in a nail nearly always affects just one nail.

Dark lines on several nails that all look the same are very likely benign.

Dr. Schlessinger adds, “The colors can be anything due to nail thickness and different areas where moles can originate.

“The most usual causes for nail issues, however, are trauma and hereditary issues.

“Make sure to tell your doctor if you have had trauma or if your family has these issues so they can evaluate you thoroughly.”

A benign area of pigmentation can actually cause a “pseudo-Hutchinson’s sign,” but if you see this sign, it’s not for you, as the patient, to diagnose.

See a dermatologist who will have it biopsied.

Dr. Schlessinger, founder of LovelySkin.com, has 25+ years of experience treating many skin conditions including melanoma. He’s founder of the Advanced Skin Research Center, a clinical facility that investigates new medications and treatments.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.  

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