Another cause of black lines on the nails is a splinter hemorrhage, which occurs when blood vessels under the fingernail are damaged, often due to injuries, such as hitting. More seriously, a black line or lines on the nails can indicate the presence of melanoma, a dangerous form of skin cancer.
What do lines on fingernails mean?
Having vertical (longitudinal) ridges on the fingernails refers to the presence of tiny raised lines or ridges that run up and down the length of the nail. Ridges are among the different kinds of nail abnormalities that can develop due to aging, nail injury, or trauma, or underlying medical conditions.
What causes black splinters under fingernails?
Splinter hemorrhages look like thin, red to reddish-brown lines of blood under the nails. They run in the direction of nail growth. The hemorrhages may be caused by tiny clots that damage the small capillaries under the nails. Splinter hemorrhages can occur with infection of the heart valves (endocarditis).