A black toenail signifies a discoloration of the nail plate, often appearing as dark blue, brown, or black hues. This common concern can stem from various sources, ranging from minor occurrences to more serious underlying health issues. While some instances of toenail discoloration are benign and resolve on their own, others may require professional medical attention.
Common Causes of Black Toenails
The most frequent reason for a toenail turning black is a subungual hematoma, which is essentially a bruise under the nail. This occurs when trauma, such as stubbing a toe, dropping a heavy object, or repetitive impact from ill-fitting shoes or activities like running, ruptures tiny blood vessels beneath the nail plate. Blood then pools under the nail, leading to the characteristic dark discoloration, which can range from red, purple, dark brown, or black as it clots and breaks down. This accumulated blood can also cause pain and discomfort, often peaking within the first few hours after the injury.
Another common cause is a fungal infection. While these infections often present with white or yellow discoloration, certain types of fungi, particularly dermatophytes, can lead to dark brown or black spots or streaks as debris builds up under the nail. They can also result in other symptoms like nail thickening, crumbling, or separation from the nail bed. These fungi thrive in warm, moist environments, making toenails particularly susceptible.
A more serious, though rare, cause of black toenails is subungual melanoma, a type of skin cancer that develops under the nail. This can appear as a brown or black streak that may widen or change over time, often without a history of injury. Unlike a bruise, which grows out with the nail, a melanoma streak typically does not heal or change positions, although it may grow larger. Though rare, its prognosis can be poorer due to delayed diagnosis.
Less commonly, certain medications can induce nail discoloration. These include some chemotherapy drugs, specific antibiotics, and retinoids. Systemic health conditions like diabetes, kidney disease, heart disease, or anemia can also contribute to nail discoloration.
Recognizing When to See a Doctor
While many instances of black toenails are not severe, certain signs warrant prompt medical evaluation to rule out serious conditions. Seek professional advice if the discoloration appeared without any known trauma or injury. This is especially true if the black area grows larger or does not grow out with the nail, unlike a bruise.
Pain, swelling, pus, or a foul odor around the toenail indicate a potential infection or significant injury requiring medical attention. Any dark streaks or bands that extend into the cuticle or the skin surrounding the nail (Hutchinson’s sign) can indicate subungual melanoma. Changes to the nail plate itself, such as thickening, crumbling, or the nail lifting away from its bed without clear cause, also require assessment. Individuals with underlying health conditions, such as diabetes, compromised immune systems, or poor circulation, should consult a doctor for any toenail changes, as they may be more susceptible to complications.
Managing and Preventing Black Toenails
For minor black toenails resulting from trauma, self-care measures can often be effective. Applying the R.I.C.E. protocol—Rest, Ice, Compression, and Elevation—can help manage fresh injuries and reduce swelling. Small subungual hematomas typically do not require treatment, as the nail grows out, pushing the discolored area forward until it can be trimmed.
Preventing black toenails involves proper foot and nail care. Wearing well-fitting shoes with ample space in the toe box is important, especially for activities involving repetitive impact like running. Trimming toenails regularly and straight across, rather than rounding the edges, also helps prevent trauma and ingrown nails. Maintaining good foot hygiene by keeping feet clean and dry can help deter fungal infections. If self-care measures do not resolve the issue, or if any concerning symptoms are present, seek professional medical advice.