Splinter hemorrhages appear as narrow, red to reddish-brown lines of blood beneath the nails. They run in the direction of nail growth and are named splinter hemorrhages because they look like a splinter beneath the fingernail. The hemorrhages may be caused by tiny clots that damage the small capillaries under the nails.

Splinter hemorrhages are associated with infection of the heart valves (endocarditis) and may be caused by vessel damage from swelling of the blood vessels (vasculitis) or tiny clots that damage the small capillaries (microemboli).

You should let a physician look at them if you haven't had any recent trauma to the nail