Dark toenails can be a cause for concern, but they are often harmless. While a change in toenail color might sometimes indicate an underlying health issue, many common reasons for discoloration are benign. Understanding the various factors that can lead to dark toenails can help determine when professional medical attention is appropriate.
Physical Injury
One of the most frequent causes of a dark toenail is a physical injury, often resulting in a subungual hematoma. This occurs when blood vessels underneath the nail rupture, causing blood to pool. Common culprits include stubbing a toe, dropping a heavy object, or repetitive micro-trauma from ill-fitting shoes during activities like running or hiking.
A subungual hematoma can appear as black, purple, or red discoloration under the nail. The initial pain or pressure from the injury subsides as the blood clots. Over time, the discolored area will gradually grow out with the nail, a process that can take several months.
Fungal Infections
Fungal infections can also lead to discoloration and other changes in toenails. These infections thrive in warm, moist environments, like inside shoes, making toenails susceptible. The fungi can cause the nail to change color, ranging from yellow, brown, or black.
Beyond discoloration, fungal infections show other symptoms. The affected nail can become thickened, brittle, or crumbly. It can also separate from the nail bed, and a foul odor can be present. Untreated fungal infections can spread or lead to discomfort.
Pigmentation Changes
Dark toenails can also result from changes in pigmentation. Melanonychia is a condition characterized by a brown or black streak running vertically down the nail. This benign condition is common in individuals with darker skin tones, as a natural variation due to increased melanin deposits.
However, a dark streak can rarely be a sign of subungual melanoma, a serious form of skin cancer that develops under the nail. Distinguishing benign melanonychia from melanoma is important. Warning signs for melanoma include an irregular border, a widening of the stripe, or changes in its color. Another indicator is Hutchinson’s sign, where the pigmentation extends beyond the nail plate onto the surrounding skin of the nail fold.
When to Seek Medical Advice
While many instances of dark toenails are harmless, certain signs warrant a visit to a healthcare professional. Seek medical attention if the discoloration appears without a clear history of injury or does not gradually grow out with the nail. A rapidly changing or spreading dark spot, especially if it has irregular borders or varies in color, requires evaluation.
Pain or swelling associated with the discoloration, or any signs of infection like pus or redness, are also reasons to consult a doctor. If you have underlying health conditions like diabetes, any changes in your toenails should be promptly checked. Early diagnosis is important for managing potentially serious conditions like melanoma.