A black, purple, or brownish discoloration under a toenail is frequently due to trauma, such as when something is dropped on the toe. The color results from a blood clot or bleeding under the nail, and may involve the entire nail or just a small portion of it. This can be very painful and we may need to drill a hole in the nail to relieve the pressure caused by bleeding. After such procedure, you sould feel the immediate relief.
Although it is very rare, a more serious cause of black toenails is malignant melanoma. Since early diagnosis and treatment of melanoma improves the chances for a good outcome, it is important that all black toenails be evaluated by a podiatrist to rule out this cause.
Other rare causes of black toenails include fungal infections, chronic ingrown nails, or health problems affecting the rest of the body.