A black discoloration on a nail can be alarming, but it is a common occurrence. A black nail can stem from various origins, ranging from minor issues to conditions requiring prompt medical evaluation. Understanding the potential causes is important for determining when professional medical attention is necessary.
Everyday Reasons for Black Nails
The most frequent reason for a nail to turn black is a subungual hematoma, a bruise under the nail. This occurs when blood vessels beneath the nail plate are damaged, leading to blood pooling. Direct trauma, such as dropping a heavy object on a toe or slamming a finger in a door, commonly causes this.
Repetitive minor trauma, like the impact from ill-fitting shoes during running or intense physical activity, can also lead to a subungual hematoma, sometimes called “runner’s toe” or “jogger’s toe.” Its color varies, initially red or purple, then turning dark brown or black as blood clots and breaks down. Pressure from trapped blood often causes pain and throbbing, which typically subsides within a few days.
Another common cause of darkened nails is a fungal infection, known as onychomycosis. While these infections often present as white or yellow discoloration, certain fungi can produce brownish or blackish hues. The nail may also become thickened, brittle, or crumbly, and an unpleasant odor may develop. Fungal infections are more prevalent in toenails and are often associated with warm, moist environments, or conditions like diabetes.
Benign longitudinal melanonychia is a non-cancerous condition that causes brown or black bands to appear lengthwise on the nail. This pigmentation results from increased melanin production by melanocytes in the nail matrix, where nail growth originates. This condition is particularly common in individuals with darker skin tones, where it is a natural and harmless occurrence. Trauma, pregnancy, and inflammatory skin conditions can also activate melanocytes, leading to longitudinal melanonychia. Unlike a bruise, these bands do not grow out with the nail or significantly change appearance unless affected by a new stimulus.
Less Common But Serious Causes
While less common, certain serious conditions can also cause a nail to turn black, requiring medical evaluation. Subungual melanoma, a rare form of skin cancer, is a concern when dark discoloration appears under the nail. This cancer originates from melanocytes within the nail matrix, similar to moles on the skin.
Subungual melanoma often presents as a brown or black streak that runs vertically along the nail. It may be irregularly shaped, widen over time, or show pigment extending to the surrounding skin (Hutchinson’s sign). The nail plate might also split, crack, or deform, and in advanced stages, bleeding or a nodule may develop. Unlike a subungual hematoma, which appears suddenly after an injury and grows out with the nail, melanoma tends to develop slowly and does not resolve as the nail grows.
Certain systemic diseases and drug reactions can also cause nail discoloration. Conditions like diabetes, kidney disease, or circulatory problems can affect nail health and sometimes cause them to turn black. Hormonal imbalances, such as Addison’s disease or hyperthyroidism, have also been associated with nail pigmentation changes. Some medications, particularly chemotherapy drugs, antimalarials, and certain antibiotics, can induce nail discoloration, presenting as brown, black, or blue-gray changes. These drug-induced changes often affect multiple nails and may appear as diffuse discoloration or distinct bands.
When to Consult a Healthcare Professional
Consult a healthcare professional if a black nail appears without known injury or if its cause is unclear. Persistent discoloration that does not grow out with the nail, or a dark streak that changes in size, shape, or color, warrants a medical visit. Any signs of infection, such as increasing pain, swelling, redness, or discharge around the nail, warrant attention. A doctor should also evaluate if the black area extends to the surrounding skin, if the nail lifts from the nail bed, or if there is bleeding, ulceration, or nodule formation under or around the nail. Individuals with underlying health conditions, such as diabetes or circulatory issues, should seek medical advice for any nail changes, as these conditions increase susceptibility to complications.
What a Doctor Will Do
When you consult a doctor about a black nail, they will begin by taking a detailed medical history, including recent injuries or medications. A physical examination of the affected nail and surrounding area will assess the discoloration and any associated symptoms. To determine the cause, the doctor may perform diagnostic tests.
For suspected fungal infections, a nail sample might be taken for a fungal culture or a potassium hydroxide (KOH) preparation to identify fungal elements under a microscope. If subungual melanoma is a concern, a nail biopsy is often necessary. This procedure involves removing a small piece of the nail matrix or nail bed for microscopic examination, crucial for distinguishing between benign conditions and cancer. Treatment may range from simple home care for minor trauma to medical procedures like draining a subungual hematoma, or specialized treatments for fungal infections or melanoma.