A black or discolored toenail is a common issue that often causes concern, but it typically signifies bleeding or a change in pigment beneath the nail plate. Medically, this condition is most frequently recognized as a subungual hematoma when caused by trauma. This discoloration is trapped between the nail plate and the nail bed beneath it. Understanding the cause and the natural resolution process provides the clearest answer to whether the discoloration will resolve on its own.
Understanding the Causes of Discoloration
The most frequent reason a toenail turns black is a subungual hematoma. This trauma can be a single, acute event, such as stubbing the toe or dropping a heavy object on it. More often, it is the result of repetitive micro-trauma, such as the toe repeatedly hitting the end of a shoe during running or hiking, which is sometimes called “runner’s toe.” This impact causes small blood vessels in the nail bed to burst, leading to a pool of blood that darkens as it clots under the nail.
While less common, other conditions can also cause the nail to darken. A fungal infection, known as onychomycosis, can sometimes lead to a black or dark brown discoloration, although it typically presents as yellow or white. The rarest, but most serious, cause is subungual melanoma, a form of skin cancer that appears as a dark streak or patch under the nail.
The Natural Resolution Process and Timeline
For a black toenail caused by a subungual hematoma, the discoloration does not fade or get reabsorbed like a typical bruise on the skin. Since the blood is trapped under the hard nail plate, the dark area must be pushed out as the nail grows. This process means the discoloration will slowly migrate from the base of the nail toward the tip over many months. The speed of resolution is entirely dependent on the natural rate of toenail growth.
Toenails grow at an average rate of approximately 1 to 1.6 millimeters per month. Because of this slow pace, a completely discolored toenail can take anywhere from six to nine months to fully grow out, and for the big toe, it may take up to 12 to 18 months. If the trauma was severe enough, the increased pressure from the pooled blood may cause the nail to loosen and eventually detach, allowing a new nail to grow in its place.
The initial management for a simple, non-painful hematoma is typically observation, allowing the body to manage the issue itself. You can track the progress of the discoloration moving up the nail. If the black area moves with the nail and eventually reaches the tip, it is a benign hematoma that is resolving naturally.
Identifying When Medical Intervention is Necessary
If the hematoma is causing intense, throbbing pain, it is due to the pressure of the trapped blood and may require drainage. A doctor or podiatrist can perform a quick procedure called trephination, which involves creating a small hole in the nail plate to release the pressure and drain the blood, providing immediate relief. This drainage procedure should ideally be done within 48 hours of the injury for maximum effectiveness.
Any black discoloration that appears without a clear history of injury should be evaluated by a healthcare professional. Additionally, if the dark area does not appear to be growing out with the nail over several months, or if the pigment spreads onto the skin surrounding the nail plate, particularly near the cuticle, it is a serious sign known as Hutchinson’s sign. This could suggest subungual melanoma and warrants immediate investigation. Signs of infection also require prompt medical intervention:
- Increasing redness
- Swelling
- Warmth
- Discharge
- Fever
Steps for Preventing Black Toenails
Preventing the most common type of black toenail involves minimizing repetitive trauma to the toes. This requires paying close attention to the fit of your footwear, especially during athletic activities. Shoes should have a wide toe box and be long enough to ensure the toes do not jam against the front, even when the feet swell during exercise. There should be a thumb’s width of space between the longest toe and the end of the shoe.
Toenails should be trimmed straight across and kept relatively short, ensuring they do not extend past the tip of the toe. Longer nails are more likely to strike the inside of the shoe repeatedly, causing micro-trauma and subsequent bruising. Wearing moisture-wicking socks can help prevent the foot from sliding forward inside the shoe, further reducing repetitive impact.