A black toenail can be a concerning discovery. While the discoloration can appear alarming, it stems from various factors, many are benign. However, it can occasionally signal a more serious underlying health condition that requires medical attention.
Trauma-Induced Discoloration
The most frequent cause of a toenail turning black is physical trauma, a subungual hematoma. This happens when blood vessels beneath the nail rupture, trapping blood under the nail plate. Common incidents include stubbing a toe, dropping a heavy object, or wearing ill-fitting shoes that cause repetitive pressure. Athletes, especially runners, often experience this from repeated impact within footwear.
Initially, a subungual hematoma may cause pain and pressure as blood accumulates beneath the nail. The discoloration typically starts as red or purple and then darkens to brown or black as the blood dries. The affected nail gradually grows out, carrying the discolored area with it; sometimes, the entire nail may loosen or fall off. This process can take several months for toenails to fully grow out.
Fungal Infections and Other Causes
Beyond trauma, fungal infections, medically known as onychomycosis, are a common reason for toenail discoloration. These infections occur when fungi invade the nail bed, often thriving in warm, moist environments. Fungal infections can cause the nail to appear yellow, brown, or even dark green or black due to debris buildup.
Symptoms often include thickening of the nail, a brittle or crumbly texture, and sometimes a foul odor. The nail may also lift away from the nail bed. While fungi are the primary culprits, other causes of toenail discoloration can include certain medication side effects (e.g., antimalarial drugs or chemotherapy) or systemic diseases like diabetes or poor circulation.
When to Be Concerned: Serious Causes and Medical Consultation
While many black toenails are harmless, certain signs warrant immediate medical attention. One serious, though rare, cause is subungual melanoma, a skin cancer developing under the nail. Unlike a bruise, the discoloration often appears as a dark brown or black streak that does not grow out with the nail and may have irregular borders. Other features include discoloration spreading to the skin around the nail (Hutchinson’s sign) or no history of trauma.
Additional red flags include severe pain or swelling that does not subside, or signs of infection like pus, redness, or warmth around the nail. Any unexplained blackening, spreading discoloration, or nail changes with other systemic symptoms should prompt a visit to a doctor or podiatrist. Early detection and diagnosis are important for effective treatment, especially in cases of subungual melanoma.
Prevention and Management
Preventing toenail discoloration involves simple practices. Wearing properly fitting shoes is important, especially for individuals engaging in activities like running or hiking, as this reduces repetitive stress on the nails. Protecting feet from direct trauma, such as dropping heavy objects, also helps prevent subungual hematomas.
Maintaining good foot hygiene is important, including keeping feet clean and dry, regularly changing socks, and avoiding walking barefoot in public damp areas where fungal infections can be acquired. Proper nail trimming, straight across and not too short, can also help. For minor trauma-induced cases, self-care may involve rest, applying ice, and elevating the foot to reduce swelling and discomfort. It is important to monitor the nail’s growth and avoid attempting home remedies like draining blood yourself, as this can introduce infection. For any persistent or concerning discoloration, professional diagnosis remains the most effective approach.