A subungual hematoma is a collection of blood or bruising under a fingernail or toenail. It is caused by damage to the blood vessels under the nail bed, which leak blood into the space between the nail and the nail bed. This is usually the result of a crush injury to the toe or fingertip, such as hitting your thumb with a hammer, stubbing your toe, or slamming your fingertips in a door. It can also be caused by repeatedly wearing too-tight shoes. This is especially true in runners or athletes in sports with repetitive stop-and-start action, which jams the toes against the end of the shoe.
After an injury, the first symptom of a subungual hematoma is usually redness and throbbing pain caused by the pressure of blood pooling under the nail bed. Then, there will be a dark discoloration under the nail, which may be red, maroon, purple, blue, black, brown, or a combination of these colours. The discoloration may take up a large or small portion of the nail, depending on severity. Often, there will also be tenderness and swelling of the affected fingertip or toe. In some cases, the nail plate may be broken or damaged, resulting in the nail pulling away from the nail bed. The nail may be yellow or opaque (solid coloured as opposed to translucent like a normal nail), and the skin under the nail may be thickened due to blood accumulation.
Any dark discoloration under the nail that does not follow a known injury should be assessed by a doctor for the possibility of a type of skin cancer called subungual melanoma.
It is not always necessary to seek medical treatment for a subungual hematoma. However, you should seek medical attention right away if the hematoma is accompanied by intense throbbing pain, excessive bleeding or swelling, or the injured finger or toe shows an obvious deformity. If symptoms do not resolve or improve after a couple of days, you may also require medical treatment.
A healthcare provider can usually diagnose a subungual hematoma by inspecting the nail and finger/toe with a history of recent injury. An x-ray may be performed to check for any fractures/broken bones. In some cases, it may be necessary to perform a procedure called nail trephination to relieve pain and pressure. This procedure involves using a sterile needle, cautery device, or laser to make a small hole (or multiple ones in a larger hematoma) in the nail to allow pooled blood to drain. If the nail is highly damaged or most of the nailbed is involved, the nail may be removed altogether. A fingernail will typically grow back within a few weeks, and a toenail may take up to a few months to regrow.
To treat a subungual hematoma at home, ice and elevation can be used to relieve pain and swelling. Ice should not be left on for more than 20 minutes at a time. Over-the-counter pain relievers can be used to help with pain and discomfort. Never try to use a heated needle or wire to drain the blood under the nail at home. The damaged nail may or may not fall off on its own with no further treatment. Healthy nails will regrow to replace the damaged/discoloured nail.
The most common complication of subungual hematoma is an infection of the injured nailbed. Redness, new swelling and tenderness, pus, drainage, warmth to touch, and fever are all signs of infection, which needs medical treatment. To prevent infection, keep the area clean, and do not attempt to drain blood under the nail at home. Most injuries causing subungual hematoma are accidental, but wearing properly fitting shoes can help prevent subungual hematomas. If you work in an environment that risks heavy objects falling on your feet, wear protective, steel-toed boots.