A black toenail refers to a discoloration of the toenail. While often a minor issue, a black toenail can sometimes signal a more serious underlying health condition that requires medical attention.
Common Causes of Black Toenails
Trauma is a frequent reason for toenail discoloration, leading to a subungual hematoma. This occurs when an impact, such as stubbing a toe or dropping an object, causes blood vessels beneath the nail to break and bleed. Repetitive pressure from ill-fitting shoes during activities like running can also cause this bruising, sometimes called “runner’s toe.” The trapped blood can cause significant pain due to pressure, and the nail may eventually separate or fall off as it heals.
Fungal infections, or onychomycosis, are another common cause. These infections often begin as white or yellow spots but can progress to dark brown or black discoloration due to debris buildup. Fungi thrive in warm, moist environments, making toenails particularly susceptible. Beyond color changes, fungal infections can cause the nail to thicken, become brittle, crumble, or lift from the nail bed, and may produce an unpleasant odor.
In rare instances, a black streak or spot under the nail could be subungual melanoma, a serious form of skin cancer. Unlike a bruise, which typically grows out with the nail, a melanoma streak may not heal, change position, or might grow larger with an ill-defined border. This discoloration can also extend into the surrounding skin or cuticle, a sign known as Hutchinson’s sign. Subungual melanoma can also lead to a thinned, cracked, or distorted nail, ulcer formation, or bleeding.
Other less common factors can contribute to toenail discoloration. Certain medications, including those used for chemotherapy, may lead to nail changes. Systemic health conditions such as diabetes, heart disease, kidney disease, anemia, or psoriasis can also impact nail health. Bacterial infections can also cause discoloration, though often a different hue.
When to Seek Medical Attention
While many black toenails are harmless and resolve on their own, certain signs warrant prompt medical evaluation. Consult a medical professional if the discoloration appears without a clear injury, or if it persists or worsens. Increasing pain, swelling, pus, or other signs of infection around the nail also indicate a need for assessment.
Pay particular attention if the black area is a streak extending into the cuticle or surrounding skin, known as Hutchinson’s sign, as this can indicate subungual melanoma. If a black toenail does not improve or grow out as expected after an injury, or if there is uncertainty about the cause, seek medical advice. Individuals with a personal or strong family history of melanoma should also be vigilant about any new or changing nail discoloration.
Diagnosis and Treatment Approaches
Diagnosing the cause of a black toenail typically begins with a visual examination and a review of the patient’s medical history, including any recent injuries. If a fungal infection is suspected, a doctor might take a nail clipping or scrape debris for laboratory culture. In cases where melanoma is a concern, a biopsy of the nail tissue will be performed to examine cells for cancerous changes.
For subungual hematomas from trauma, minor cases may not require specific treatment, as discoloration grows out with the nail. If the hematoma is large and causing significant pain due to pressure, a procedure called trephination can be performed. This involves creating a small hole in the nail plate to drain trapped blood, quickly relieving pressure and pain. In more severe cases involving extensive damage or suspected nail bed laceration, the nail plate might need removal for surgical repair.
Treatment for fungal infections often involves antifungal medications. Topical solutions, creams, or lacquers can be applied directly to the nail, though these are generally more effective for mild cases. Oral antifungal medications, such as terbinafine or itraconazole, are typically prescribed for more severe infections, offering higher cure rates but requiring several months of treatment. Laser therapy is another option, sometimes used in combination with topical antifungals.
If subungual melanoma is diagnosed, primary treatment involves surgical removal of the affected nail and sometimes part of the digit. Early detection is important for a better prognosis, as melanoma can spread if left untreated. Depending on the stage and spread, additional treatments like radiation therapy, chemotherapy, or immunotherapy may be recommended.
Preventing Black Toenails
Preventing black toenails involves proper footwear and foot hygiene. Wearing correctly fitting shoes is important, especially for athletic activities, ensuring ample room in the toe box to prevent repetitive trauma or pressure. Athletes may benefit from sport-specific shoes designed to absorb impact.
Maintaining good nail care also helps reduce the risk. This includes trimming toenails regularly, keeping them short and cut straight across to avoid ingrown nails or catching them on footwear. Proper foot hygiene is important for preventing fungal infections. Keeping feet clean and dry, especially after showering or swimming, discourages fungal growth.
Wearing protective footwear like flip-flops or shower shoes in public areas such as locker rooms, gyms, and swimming pools can help prevent exposure to fungi. Choosing socks made of moisture-wicking materials can also help keep feet dry. Regularly inspecting and replacing shoes when necessary also contributes to prevention.