A black nail is a discoloration under the nail plate. It can range from dark blue to black. While often minor, it can signal a more significant underlying condition. Understanding causes helps determine if attention is needed.
Causes of Black Nails
The most frequent reason for a black nail is a subungual hematoma: bleeding and bruising under the nail. This often results from direct impact, like dropping a heavy object or stubbing a finger. Repetitive microtrauma, like from ill-fitting shoes in runners, can also cause this injury by rupturing small blood vessels. The trapped blood appears black or dark purple, similar to a skin bruise.
Fungal infections (onychomycosis) can also cause dark brown or black nail discoloration. They thrive in warm, moist environments, causing the nail to thicken, become brittle, and change color. Darkness may be from debris or the fungus. These infections can spread if untreated.
Less commonly, a black nail can indicate subungual melanoma, a rare skin cancer under the nail. It often appears as a dark, vertical band or streak that widens. Unlike a hematoma, melanoma typically appears without injury and does not grow out with the nail. Rarely, certain systemic diseases or medications can also cause nail discoloration.
Treating Black Nails and When to See a Doctor
For black nails from minor trauma, self-care is often sufficient. Apply ice immediately after injury to reduce swelling and bleeding. Elevating the limb also minimizes blood pooling and throbbing pain. The discoloration typically grows out with the nail over several months as new, healthy nail replaces the damaged portion.
Do not attempt to drain a subungual hematoma at home due to infection risk. However, if pain is severe and throbbing from pressure, a healthcare professional might perform trephination. This involves creating a small hole to release trapped blood, providing immediate pain relief. This procedure must be done by a medical professional in a sterile environment.
Seek professional medical help if:
The black discoloration covers a large nail portion, causes intense pain, or shows infection signs like pus, redness, or increased swelling.
Any black discoloration appears without known injury.
A dark, vertical stripe changes or grows.
You have underlying health conditions, like diabetes or circulatory issues, as these can affect healing and increase infection risk.
If a fungal infection is suspected, a doctor can prescribe topical or oral antifungal medications. These treatments eliminate the fungus, allowing healthy nail growth. Treatment duration varies, often several months, until the infected nail is replaced by clear nail.
Preventing Black Nails
Preventing black nails often involves protecting the feet and hands from injury and maintaining good hygiene.
Wearing properly fitting shoes is important, especially for activities with repetitive foot impact like running. Too-tight or too-loose shoes cause friction and pressure on nails, leading to trauma. Ensure adequate toe box space to prevent toes hitting the shoe front.
Protecting nails from direct impact is another prevention strategy. When working with heavy objects or in activities where hands or feet might be struck, wear protective footwear (e.g., steel-toed boots or gloves) to reduce injury risk. Awareness of surroundings also helps prevent accidental trauma.
Good nail hygiene also contributes to prevention. Keep nails trimmed to a moderate length to reduce catching or undue pressure. Regularly clean nails and ensure feet are dry to prevent fungal infections, which cause discoloration and problems. Promptly addressing existing fungal infections also prevents significant discoloration or spreading.