A subungual hematoma is a collection of blood in the space between the nail bed and fingernail. Subungual hematomas result from a direct injury to the fingernail. The pressure generated by this collection of blood under the nail causes intense pain. Hematoma is generally defined as a collection of blood outside of blood vessels. Most commonly, hematomas are caused by an injury to the wall of a blood vessel, prompting blood to seep out of the blood vessel into the surrounding tissues. A hematoma can result from an injury to any type of blood vessel (artery, vein, or small capillary). A hematoma usually describes bleeding which has more or less clotted, whereas a hemorrhage signifies active, ongoing bleeding. Hematoma is a very common problem encountered by many people at some time in their lives. Hematomas can be seen under the skin or nails as purplish bruises of different sizes.