Black, dark brown, or reddish streaks beneath your nail may seem like quite the cause for concern. However, they’re usually the result of a trauma to the nail, such as accidentally closing a door on your fingertips. In these cases, the discoloration you see occurs when blood vessels under the nail bed break. (They’re called splinter hemorrhages.)
That said, these dark streaks can be caused by health conditions, including psoriasis and endocarditis (an infection in the heart).
Black streaks may also be the result of melanoma, the most serious type of skin cancer. “In these cases, the black line is much cleaner-looking than that from a trauma or broken blood vessels. Melanoma develops in melanocytes, the skin cells that produce melanin, the pigment that gives skin its color—hence the dark discoloration.
Since melanoma is incredibly serious, we recommends making an appointment with us at the first sight of any black streaks or lines just to be safe.