A black toenail can be a surprising discovery, often prompting concerns about its origin. While its appearance might seem alarming, a darkened toenail frequently stems from relatively harmless causes, though it can occasionally signal a more serious underlying condition.
Black Toenails from Injury
The most frequent reason for a black toenail is an injury, leading to a subungual hematoma. This occurs when blood vessels beneath the nail rupture, causing blood to collect under the nail. Common injuries include dropping a heavy object, stubbing a toe, or repetitive trauma from ill-fitting shoes. The trapped blood often results in throbbing pain and tenderness.
The discolored area typically appears black, blue, or purple, and its appearance may change as the blood breaks down. As the nail grows, the discoloration gradually moves outwards, eventually disappearing as the nail is trimmed. This process can take several months, often six to nine months for toenails. For minor cases, at-home care involves resting the foot and applying ice to reduce swelling and pain.
Fungal Infections of the Nail
Another common cause of nail discoloration, including black tones, is a fungal infection, medically known as onychomycosis. While fungal infections often cause nails to appear yellow, white, or brown, certain fungi or debris under the nail can lead to a black or dark green/brown appearance. The infection typically begins as a small spot and spreads over time.
Beyond discoloration, fungal nail infections present with other characteristic symptoms. These include significant thickening, a brittle or crumbly texture, and a distorted nail shape. The infected nail may also separate from the nail bed or emit a foul odor. Risk factors include prolonged exposure to warm, moist environments (e.g., tight shoes, public areas) and certain health conditions like diabetes. Fungal infections generally require medical diagnosis and targeted treatment, as they do not typically clear on their own.
Other Potential Causes
Less common but potentially serious causes can also lead to a black toenail, with subungual melanoma being a concern. This rare form of skin cancer develops under the nail, often appearing as a brown or black streak. Unlike a bruise, a melanoma streak typically does not heal or grow out with the nail and may widen or change color over time. A particularly concerning sign is Hutchinson’s sign, where pigmentation extends from the nail plate onto the surrounding skin, such as the cuticle or nail folds.
Other indicators of subungual melanoma include nail bleeding, thinning, cracking, distortion of the nail plate, or the formation of an ulcer or nodule under the nail. While rare, early detection is important due to its potential to spread rapidly without timely treatment. Certain medications, like chemotherapy drugs, or systemic diseases such as diabetes or circulatory problems, can also contribute to nail discoloration, though these are less frequent causes for a black appearance.
When to Consult a Healthcare Professional
Consult a healthcare professional for a black toenail under several specific circumstances. If the black discoloration appears suddenly without clear injury or known trauma, medical evaluation is recommended. Seek professional attention if you experience severe pain, throbbing, or pressure under the nail, especially after an injury, as this might indicate a need for drainage to relieve pressure.
Signs of infection, such as pus, increased redness, swelling around the nail, or fever, warrant immediate medical assessment. A healthcare provider should also examine the nail if the black area grows, changes shape, or if the discoloration extends into the surrounding skin (Hutchinson’s sign). If the discoloration does not improve or grow out with the nail over several months, or if multiple nails are affected without a clear cause, a professional opinion is important to rule out underlying conditions.