A toenail that appears black, or sometimes dark brown, purple, or reddish, indicates changes within the nail plate or the tissue beneath it (the nail bed). While often alarming, the causes vary from benign to those requiring medical attention. Understanding these causes helps determine the appropriate action.
Common Causes
Trauma frequently causes a black toenail, often as a subungual hematoma. This happens when an impact, like stubbing a toe or dropping an object, causes blood to pool under the nail, appearing as a dark bruise. Repetitive friction or pressure from activities like running or ill-fitting shoes can also lead to this injury. The discoloration typically grows out as the nail grows and the blood is reabsorbed.
Fungal infections, or onychomycosis, are another common cause of toenail discoloration. Fungi can invade the nail, leading to color changes from yellow or brown to black. This dark appearance may result from debris under the nail or pigment produced by the fungus. Toenails are susceptible because shoes and socks create a warm, moist environment conducive to fungal growth.
Less Obvious Factors
A black toenail may also indicate less common but more serious issues. Melanoma, a severe skin cancer, can rarely appear as a dark streak or discoloration under the nail, known as subungual melanoma. This cancerous change typically appears as a brown or black vertical band that may widen, have irregular borders, and extend to the surrounding skin. Unlike a bruise, this discoloration does not grow out with the nail or resolve on its own.
Certain medications can also cause nail discoloration as a side effect. Chemotherapy drugs, antimalarial medications, and specific antibiotics are known to cause changes in nail pigmentation. These effects are usually generalized, affecting multiple nails, and resolve after the medication is discontinued.
Bacterial infections may cause a blackish or dark green discoloration of the nail. These infections often occur with symptoms like pain, swelling, or pus. In rare cases, systemic medical conditions, such as heart or kidney diseases, or nutritional deficiencies, can contribute to nail discoloration.
When to Seek Medical Advice
While many black toenails resolve spontaneously, certain indicators warrant medical evaluation. Persistent or worsening discoloration without a clear traumatic cause needs attention. Increasing pain, swelling, or pus around the nail can signal an infection requiring treatment.
A dark streak extending from the nail plate onto the cuticle or surrounding skin (Hutchinson’s sign) is concerning for subungual melanoma and requires immediate assessment. If discoloration doesn’t improve or grow out over several months, or if melanoma or a serious underlying condition is suspected, consult a doctor. A medical professional can examine the nail, drain trapped blood, or perform a biopsy to determine the cause.
Prevention Strategies
Preventive measures can reduce the likelihood of toenails turning black. Wearing properly fitting shoes is a primary step, as footwear that is too tight or too loose can cause repetitive trauma. Ensuring adequate toe room, especially during physical activities, helps prevent toes from repeatedly hitting the shoe’s end.
Protecting feet from direct impact is also important, such as by wearing protective footwear where objects might be dropped. Good nail care habits are beneficial, including trimming toenails straight across and at a moderate length to prevent trauma and reduce fungal infection risk. Regular cleaning and drying of feet, especially between the toes, helps inhibit fungi and bacteria. Addressing minor foot or nail issues promptly can prevent them from escalating.