A black toenail can be a concerning discovery. While this discoloration is frequently harmless, resulting from common occurrences, it can sometimes signal a more significant underlying issue. Understanding the various reasons a toenail might turn black can provide clarity and help determine when professional medical attention is appropriate.
Understanding Physical Injury
The most frequent cause of a black toenail is physical trauma, resulting in a subungual hematoma. This occurs when blood vessels beneath the nail rupture, where blood collects. Common ways this happens include stubbing a toe, dropping a heavy object on the foot, or even repetitive impact from activities like running or wearing ill-fitting shoes.
The pooling blood initially appears red or purple, then darkens to brown or black as it clots under the nail. This can cause pain and a feeling of pressure as the blood accumulates. In most cases, the discoloration will gradually grow out with the nail, which can take several months, typically around 6 to 12 months.
Infections and Discoloration
Beyond injury, infections can also cause toenail discoloration. Fungal infections, known as onychomycosis, are a common culprit. These infections thrive in warm, moist environments and can cause the nail to thicken, become brittle, or even crumble.
While fungal infections often present with white or yellow discoloration, a black appearance can occur due to debris buildup under the nail or from specific types of fungi. Other symptoms might include an unpleasant odor or the nail separating from its bed. Prompt treatment of fungal infections can prevent them from spreading and causing further damage.
Serious Medical Considerations
While less common, a black toenail can occasionally indicate a more serious medical condition, such as subungual melanoma. This rare skin cancer develops under the nail, often appearing as a dark brown or black streak running vertically from base to tip. Unlike a bruise, this discoloration often does not heal or grow out with the nail and may spread to the surrounding skin.
Other signs of subungual melanoma can include changes in the streak’s size or shape, bleeding from the nail, or the nail separating from its bed. Systemic health conditions, such as diabetes, kidney disease, heart disease, or certain autoimmune disorders, can also rarely lead to nail discoloration. These conditions can affect circulation or nail health, contributing to changes in appearance.
Knowing When to Seek Professional Help
Seek medical evaluation for a black toenail, especially if the cause is unclear or concerning symptoms are present. Specific warning signs that warrant a visit to a healthcare provider include persistent or increasing pain, signs of infection like pus, redness, or swelling, or if the discoloration spreads beyond the nail itself. A medical professional should also assess any changes in nail shape or texture not clearly linked to an injury.
If the black discoloration appeared without any known trauma, or if it does not improve as the nail grows, professional advice is recommended. A doctor can accurately diagnose the cause, differentiate between a harmless bruise and a more serious condition like melanoma, and provide appropriate treatment options. This may involve draining a painful hematoma, prescribing antifungals for an infection, or performing a biopsy for suspicious lesions.