Among the most common causes of dark and discolored toenails are subungual hematoma and fungal infection. In rare cases, the discoloration on the toenail is cancerous in nature and is called subungual melanoma.
Subungual hematoma refers to a condition where there is bleeding underneath the toenails on the nail bed. This is often caused by direct impact on the toe, such as hitting it on a hard surface or a heavy object being dropped on the toe. Immediately after the injury, the symptoms include extreme and throbbing pain on the injured area as blood collects under the nail.
Although subungual hematoma often does not cause any serious complications, it will still be best to consult a medical professional to rule out any broken bones or serious injuries in the surrounding tissues. Should discoloration that looks similar to a subungual hematoma appear on the toenails, without any history of trauma, it should immediately looked at by a physician to rule out tumor under the nail bed.
Fungal infection can also cause toenails to take on a dark color. The discoloration happens when debris accumulates under the nail. The most effective way to treat discolored nails is to just grow out the nails. In the case of subungual hematoma, the pooled fluids under the nail can also be drained out if it is causing too much pain and discomfort.