what causes blue toenails
Black-and-Blue Toenails (Hematoma). Unlike with yellow toenails, black-and-blue toenails are not actually caused by a change in the color of the nail enamel itself. Black-and-blue toenails are caused by an injury to the skin beneath the toenail. As blood and fluid collect beneath the nail plate the nail itself, which is somewhat translucent, begins to appear black.