A black line on your nail (medically known as melanonychia) causes a streak of dark pigmentation that runs along the nail bed ...

Also, the cuticular seal of the nails should be intact, and the nail plate should adhere to the nail bed, says Dr. Thomas ...

"A brown or black streak on a nail is known as melanonychia," Weiss says. "This should always be diagnosed by a certified dermatology provider as you want to make sure to rule out something more ...

or black nail plate discoloration and is usually not tender. The differential diagnosis of subungual hematoma includes benign and malignant tumors, longitudinal pigmented band (melanonychia ...

However, these lines could also result from nail psoriasis or longitudinal melanonychia (effectively a mole of the nail), Stringer says. In extreme cases, these lines may turn out to be a squamous ...