A discolored toenail can be a concerning sight, but the black or dark appearance is most often the result of a subungual hematoma, which is simply blood trapped beneath the nail plate. This common issue arises from trauma to the toe, and the resulting discoloration is essentially a bruise under the nail. While many cases resolve naturally, determining the exact cause of the discoloration is the necessary first step before deciding on any treatment.
Identifying the Underlying Cause
A black toenail is typically caused by trauma, categorized into two main types. Acute trauma occurs from a single, forceful impact, such as dropping a heavy object on the toe, causing immediate bleeding under the nail bed and forming a subungual hematoma. The second type is repetitive microtrauma, often seen in athletes like runners, where the toe constantly jams against the inside of a shoe, leading to chronic bruising over time.
Other factors can also lead to a darkened nail, including fungal infections, which may appear brown, yellow-black, or gray, often accompanied by thickening or crumbling of the nail. Certain systemic health conditions, such as diabetes or anemia, can also affect nail color. In rare instances, a persistent dark streak or spot may indicate subungual melanoma, a serious form of skin cancer that requires immediate medical evaluation.
Managing Minor Black Toenails at Home
For minor trauma with manageable pain, initial care should focus on minimizing swelling and discomfort. The RICE protocol—Rest, Ice, Compression, and Elevation—is the recommended immediate response for a subungual hematoma. Resting the injured foot and applying an ice pack wrapped in a cloth for 20 minutes at a time helps reduce both swelling and pressure.
Elevation of the foot above the heart also assists in reducing swelling. Over-the-counter pain relievers like ibuprofen can manage discomfort and inflammation. Monitor the nail for any changes in pain level or signs of infection as the injury heals. Attempting to drain a subungual hematoma at home is strongly advised against due to the high risk of introducing infection.
Critical Indicators for Seeking Medical Treatment
Any black toenail that appears without a known injury should be evaluated, as this raises suspicion for non-traumatic causes, including melanoma. Severe, throbbing pain that does not lessen with at-home care, or pain suggesting significant pressure under the nail, often warrants professional drainage to relieve the pressure.
Signs of infection, such as increasing redness, warmth, pus draining from under the nail, or a fever, indicate a need for prompt medical treatment. Discoloration that covers more than 25% of the nail plate is also a threshold for seeking professional advice. Hutchinson’s sign, where the dark pigment extends from the nailbed into the skin of the cuticle or nail fold, is a particularly concerning indicator of subungual melanoma.
The Healing Process and Future Prevention
Healing a black toenail caused by trauma is lengthy, as the discolored area must grow out with the nail. A toenail grows slowly; it can take six to nine months for a smaller toenail to fully replace itself, and up to 12 to 18 months for the big toenail to completely regrow. If the pressure was significant, the damaged nail may eventually lift or fall off entirely, which is a natural part of the healing as the new nail forms underneath.
While waiting for the nail to regrow, preventative measures are necessary to avoid a recurrence, especially for athletes who experience repetitive microtrauma (“runner’s toe”).
Preventative measures include:
- Ensuring proper shoe sizing, allowing a thumbs-width of space between the longest toe and the end of the shoe.
- Wearing well-fitting, sport-specific footwear.
- Trimming toenails straight across and keeping them even with the end of the toe to prevent trauma.
- Practicing consistent foot hygiene and wearing moisture-wicking socks to prevent fungal infections.
- Maintaining a balanced diet with proper nutrients, such as biotin, to support new nail health.