Dark toenails are a common concern. This change in nail appearance can be unsettling, as it can stem from various causes, ranging from harmless incidents to more serious underlying health issues. Understanding these potential reasons helps determine the appropriate course of action.
Physical Injury and Bruising
A frequent cause of a dark toenail is a subungual hematoma, which occurs when blood becomes trapped under the nail plate. This condition typically results from direct trauma, such as stubbing a toe or dropping a heavy item. Ill-fitting footwear can also contribute, as shoes that are too tight or too loose can cause repetitive micro-trauma to the nail, particularly impacting the big toe during activities like walking or running. The discoloration often appears immediately or within hours of the injury, manifesting as black, blue, or purple hues under the nail.
The color change is due to the pooling of blood, which gradually darkens as it clots and ages. This type of bruising can be painful due to pressure buildup under the rigid nail. As the nail grows out, the discolored area will slowly migrate towards the tip, eventually growing off with the nail. If the pressure is severe, a healthcare professional might need to drain the blood to alleviate pain, a procedure known as trephination.
Fungal and Other Infections
Fungal infections, medically known as onychomycosis, are another common reason for toenail discoloration, which can sometimes include dark hues. These infections thrive in warm, moist environments, making feet particularly susceptible. The fungi, often dermatophytes, can penetrate the nail plate, leading to changes in its texture and color. While frequently causing yellow, white, or brown discoloration, they can also present as dark brown or black, especially if debris accumulates under the nail or if the infection is longstanding.
Beyond color changes, fungal infections often cause the nail to thicken, become brittle, or crumble at the edges. The nail might also lift from the nail bed, a condition called onycholysis. Bacterial infections can also affect the nail unit, potentially leading to discoloration, often associated with green or black hues, and may involve pain, swelling, or pus. These infections usually require specific treatments to prevent further damage or spread.
Underlying Medical Conditions and Medications
Darkening toenails can signal broader health concerns, including certain systemic medical conditions. For instance, individuals with diabetes may experience changes in nail health due to impaired circulation and nerve damage, making them more prone to infections and discoloration. Kidney disease can also affect nail appearance, sometimes causing a half-and-half nail or other pigmentary changes. Rare autoimmune conditions might also manifest with nail abnormalities, including changes in color.
A more serious, though rare, cause of a dark toenail is subungual melanoma, a form of skin cancer that develops under the nail. This condition often appears as a dark, expanding stripe or patch that may involve the nail fold, a sign known as Hutchinson’s sign. Unlike a bruise, a melanoma typically does not grow out with the nail and may change in size or color over time. Certain medications can also induce nail discoloration as a side effect, including some antimalarial drugs, chemotherapy agents, and antibiotics.
When to Seek Medical Attention
Consult a healthcare professional if you notice a dark toenail, especially when the cause is not immediately clear. Seek medical attention if the discoloration persists without a clear history of injury, or if a dark spot under the nail changes in size, shape, or color. Persistent pain, swelling, redness, or signs of infection such as pus around the nail also warrant a medical evaluation. If you suspect an infection or if the nail appears to be lifting from the nail bed, professional assessment is recommended. Early diagnosis and intervention are important, particularly for conditions like subungual melanoma, where timely treatment can affect outcomes.