Toenail fungus, medically known as onychomycosis, is a common condition that can cause various changes in the appearance of your toenails. While often associated with white or yellow discoloration, a black appearance can be particularly concerning. Understanding the underlying reasons for this black discoloration is important for proper management and for distinguishing it from other potential causes of dark nails.
How Toenail Fungus Can Cause Black Discoloration
Toenail fungus can lead to black discoloration through several mechanisms. One way is through specific types of fungi known as dematiaceous fungi. These fungi naturally produce melanin, a dark brown to black pigment. When these pigmented fungi infect the nail, their presence directly results in a dark discoloration of the nail plate.
Another factor is the accumulation of fungal debris and dirt under the nail. As the infection progresses, it can cause the nail to thicken and crumble, creating spaces where dead skin cells, fungal material, and external dirt collect. This buildup can appear dark or black, especially when trapped beneath the nail plate.
Secondary bacterial infections can also play a role in darkening a toenail. The damaged nail and surrounding skin can become susceptible to bacterial invaders. Certain bacteria produce pigments that lead to green or black discoloration of the nail.
The fungus can also cause minor trauma, leading to bleeding under the nail. As the fungus invades and lifts the nail plate, blood vessels can rupture. The trapped blood oxidizes, changing color from red or purple to dark brown or black, similar to a bruise.
Other Reasons for Black Toenails
While toenail fungus can cause black discoloration, other conditions can lead to a similar appearance. One common non-fungal cause is a subungual hematoma, a bruise under the nail. This occurs when trauma, such as stubbing a toe or repetitive pressure from ill-fitting shoes, causes blood vessels beneath the nail to break and bleed. The trapped blood then darkens. Unlike fungal discoloration, a subungual hematoma typically resolves as the nail grows out over several months.
A more serious, though rare, cause of a black toenail is subungual melanoma, a type of skin cancer that develops under the nail. This condition presents as a dark brown or black streak that may widen over time or involve the skin surrounding the nail, a sign known as Hutchinson’s sign. Unlike a bruise, the discoloration from melanoma will not grow out with the nail. It can also be accompanied by a thinning or cracking nail plate, bleeding, or a nodule under the nail.
Certain medications can also induce nail discoloration. Chemotherapy drugs, some antibiotics, and retinoids are examples that may cause changes in nail pigmentation. These drug-induced changes often appear as transverse or longitudinal bands of brown or black on the nail. Underlying systemic health conditions such as diabetes, kidney disease, heart disease, or anemia can also lead to black toenails.
When to See a Doctor About a Black Toenail
It is important to know when to seek medical evaluation for a black toenail. If the black discoloration appears suddenly without clear history of trauma or injury, a doctor’s visit is warranted. Similarly, if the black spot or streak on the nail is growing, changing shape, or extending to the skin around the nail, professional assessment is advised. These changes could indicate a more serious underlying condition, such as subungual melanoma.
Persistent discoloration that does not improve over time or with at-home care also suggests a medical opinion is needed. If the black toenail is accompanied by pain, tenderness, swelling, redness, or discharge, these symptoms may point to an infection or other complication. Individuals with underlying health conditions like diabetes, compromised immune systems, or circulatory problems should also consult a doctor for any toenail changes. A medical professional can accurately diagnose the cause through examination and, if necessary, laboratory tests.
Managing Toenail Fungus and Preventing Recurrence
Effective management of toenail fungus involves treatment and preventive measures. For mild infections, over-the-counter antifungal creams, ointments, or polishes like clotrimazole or terbinafine may be effective. These topical treatments are applied directly to the infected nail and surrounding skin. They often require consistent use for several months to show improvement, as the new, healthy nail must grow out.
For more severe or persistent fungal infections, prescription-strength treatments are necessary. Oral antifungal medications, such as terbinafine or itraconazole, are often prescribed and are more effective than topical options. These medications work systemically to clear the infection. Treatment courses can range from 6 to 12 weeks for toenail infections, but complete resolution may take several months as the nail fully grows out.
Preventing recurrence of toenail fungus involves consistent foot hygiene and lifestyle adjustments. Keeping feet clean and thoroughly dry, especially between the toes, is important as fungi thrive in warm, moist environments. Wearing breathable footwear and changing socks daily helps maintain a dry environment. Trimming nails straight across and keeping them short can prevent fungi from collecting underneath. Regularly disinfecting nail clippers and avoiding walking barefoot in public areas like locker rooms or swimming pools reduces the risk of infection.