A black toenail can be a concerning observation, often prompting individuals to seek understanding about its cause. This discoloration can arise from a range of factors, some being minor and temporary, while others may indicate a more significant underlying issue. Understanding the various possibilities is important for determining appropriate next steps.
Physical Injury and Fungal Infections
A common reason for a black toenail is physical injury, causing a subungual hematoma. Trauma, like stubbing a toe, dropping an object, or ill-fitting shoes, ruptures blood vessels under the nail. Trapped blood pools beneath the nail plate, appearing black, blue, or purple. This discoloration typically resolves as the nail grows out and is trimmed.
Repetitive microtrauma, common in athletes or those with frequent foot impact, also causes subungual hematomas. Activities like running, hiking, or prolonged standing can cause toes to repeatedly hit the inside of shoes, leading to accumulated bleeding. The nail often remains intact, but discoloration can persist for months until the damaged portion grows out.
Fungal infections (onychomycosis) are a common cause of toenail discoloration. While often yellow or white, some fungal species produce pigments turning the nail dark brown or black. These fungi thrive in warm, moist environments, breaking down the nail plate’s keratin. As infection progresses, the nail may become thickened, brittle, crumbly, or distorted.
Fungal discoloration is usually gradual, unlike immediate onset from injury. Infections can affect part or all of the nail, sometimes spreading to other nails or surrounding skin. Identifying a fungal infection often requires a medical professional to examine the nail and take a sample for analysis.
Underlying Medical Conditions
Less common, certain medical conditions can lead to a black toenail, some requiring prompt attention. Subungual melanoma is a rare but serious skin cancer appearing as a dark streak or patch under the nail. This melanoma originates in melanin-producing cells beneath the nail plate.
Unlike a bruise, a melanoma streak often appears without trauma and may gradually widen or change color. A key indicator is pigment spread to the skin surrounding the nail, particularly the cuticle or nail fold (Hutchinson’s sign). Early detection is important, making medical evaluation crucial for any suspicious or changing dark marks under the nail.
Bacterial infections can cause toenail discoloration, though typically accompanied by other symptoms. Certain bacteria, like Pseudomonas aeruginosa, produce a greenish-black pigment under the nail. This infection often presents with inflammation signs, such as pain, swelling, redness, or pus around the nail.
In rare instances, systemic diseases or medications can change nail color, including darkening. Conditions affecting blood circulation or clotting disorders can manifest as nail discoloration. Specific medications, like certain chemotherapy drugs or antimalarials, have also been reported to cause nail pigmentation changes as a side effect. These instances are generally identified within a broader medical history and ongoing treatments.
When to Consult a Doctor
Consult a medical professional if a black toenail appears without clear trauma, especially if discoloration developed gradually or you cannot recall an injury. Evaluation can differentiate between benign and more serious conditions.
Seek medical attention if the dark spot under the nail rapidly changes size, shape, or color. Any dark streak extending from under the nail to the surrounding skin, especially the cuticle or nail fold (Hutchinson’s sign), warrants immediate evaluation for subungual melanoma.
Other concerning symptoms prompting a doctor’s visit include persistent pain, swelling, redness, warmth, or pus around the affected toenail. These signs suggest a possible infection requiring specific treatment. If the nail lifts or separates from the nail bed without clear cause, or if a fungal infection isn’t improving with over-the-counter remedies, professional advice is beneficial.
Managing and Preventing Black Toenails
For minor black toenails from injury, basic home care involves keeping the area clean and dry. Allowing the nail to grow out naturally is the recommended approach, as discoloration gradually moves forward with nail growth. Avoid attempting to drain blood from under the nail at home, as this can introduce infection and should only be performed by a medical professional.
Preventing black toenails involves good foot care and appropriate footwear. Ensuring shoes fit properly, with enough toe box room to prevent pressing, is crucial, especially during physical activities. Regularly trimming toenails straight across, rather than rounding corners, helps prevent ingrown nails and reduces pressure on the nail plate.
Maintaining good foot hygiene (keeping feet clean, dry, and changing socks regularly) helps prevent fungal infections. Wearing protective footwear in environments where foot injuries are common, like construction sites or moving heavy objects, reduces trauma risk. Promptly addressing underlying foot conditions, such as athlete’s foot, contributes to overall nail health.