There are many causes for black toenails. The most common reason for the toenails to turn black is the development of blood under the nail. The medical term for this is subungual hematoma. "Sub" meaning under, "ungual" is the term for nail and "hematoma" is a localized collection of blood. The typical reason for development of blood under the nail is direct trauma. The toenail pictured here shows black discoloration at the tip and red discoloration at the bottom. This is a result of direct trauma from a football cleat.
Black toenails are also commonly the result of microtrauma. This is a common occurence in runners, especially trail runners and hill runners. The constant jamming on the toenails from the shoes causes small vessels to break under the nails allowing accumulation of blood underneath the nail. The picture shown here is a large blood blister formed under and around the great toenail in a Western States 100 mile finisher.
Large or small collections of blood can develop under the nail. This can occur after a single run, or slowly develop over a number of runs. Shoes that do not fit properly are the most common cause. When the shoes are too tight, the shoes place constant pressure on the toenails. When the shoes are too loose, the foot slides and jams into the front of the shoe. This is common when running down hills or on uneven surfaces. More information on foot injuries in runners.
Toenail fungus can also cause black toenails. Fungal toenails typically worsen over time and generally start as white splotchy areas, thickening or yellow discoloration. But, fungal nails can cause also become brown or even black. In this picture to the right, the nail is a deep yellow-brown with some black areas. This is a more advanced toenail fungus. More information on toenail fungus.
For most cases, there is no treatment needed. If there is associated pain or infection, the blood may need to be drained or the nail removed. Many times the nail will fall off on it's own after the injury. A new nail will grow in, but it may take 6-8 months to fully grow, depending on the nail. In rare cases, the black discoloration could be a melanoma. If a black area appears under the nail and there is no history of trauma, microtrauma or fungus, then make sure to have the nail evaluated by a podiatrist. If the black area is moving up the nail as the nail grows out, it is most likely not melanoma. But, your doctor may want to biopsy the area if he or she finds it suspicious.
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last updated 6/24/10
Disclaimer: The advice on this website is not intended to substitute for a visit to your health care provider. We will not be held liable for any diagnosis made or treatment recommended. Consult your doctor if you feel you have a medical problem.