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, and founder of LovelySkin.com.

“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.

“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.”




“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.

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

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

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, the patient, to diagnose. See a dermatologist who will have it biopsied.

dr. schlessingerDr. Schlessinger has 25+ years of experience treating a wide variety of skin conditions including melanoma. He’s founder of the Advanced Skin Research Center, a clinical facility that investigates new medications and treatments.