A black toenail can be concerning. While often minor, it can sometimes signal underlying conditions that warrant attention. Understanding common reasons for toenail discoloration helps recognize when it’s harmless and when to seek professional advice.
Understanding Trauma-Induced Discoloration
Physical trauma is one of the most frequent causes of a black toenail, known as a subungual hematoma. This occurs when blood vessels beneath the nail bed rupture, causing blood to pool and clot under the nail plate. The discoloration typically appears black, dark purple, or dark red, much like a bruise.
Impacts such as stubbing a toe, dropping a heavy object on the foot, or wearing ill-fitting shoes can trigger this condition. Repetitive microtrauma, common in activities like running or hiking, can also lead to subungual hematomas, often referred to as “runner’s toe.” The pressure from the trapped blood can cause pain and tenderness. As the nail grows out, the discolored area will gradually move forward and eventually disappear, a process that can take several months or up to a year.
Fungal and Bacterial Causes
Beyond trauma, infections can also contribute to toenail discoloration. Fungal infections, known as onychomycosis, are a common culprit. These infections typically begin as white or yellow spots but can progress to cause brown or black discoloration due to debris buildup under the nail. The nail may also become thickened, brittle, or crumbly. Fungi thrive in warm, moist environments, making toenails particularly susceptible.
Bacterial infections can also lead to dark spots or streaks, sometimes accompanied by pain, redness, swelling, or pus. While less common than fungal infections, bacterial involvement can occur, especially with an open wound or compromised nail integrity. Differentiating between fungal and bacterial causes is important, as symptoms vary.
Other Medical Explanations
Other medical conditions can also manifest as a black toenail. Melanoma, a type of skin cancer, can appear as a dark streak or spot under the nail, often without any history of trauma. This subungual melanoma typically presents as a brown or black vertical band that may widen over time or have irregular borders. Unlike a bruise, a melanoma streak will not heal or grow out with the nail.
Certain medications, such as minocycline, can also cause nail discoloration. Systemic diseases like diabetes, kidney disease, heart disease, or anemia can also impact nail health and lead to changes in color. While less frequent, their severity warrants consideration, especially if more common causes are ruled out.
When to Consult a Healthcare Professional
Deciding when to seek medical advice for a black toenail is important. Seek medical advice if the toenail turned black without injury, as this could indicate a serious underlying issue. Persistent or increasing pain, along with signs of infection like redness, swelling, or pus around the nail, requires medical attention.
If the discoloration spreads or extends to the surrounding skin, seek professional evaluation. Similarly, if the dark streak runs from the cuticle to the nail tip and does not grow out, or if there is a history of skin cancer, consult a doctor. Consulting a doctor ensures an accurate diagnosis and appropriate management plan.