A black toenail, while frequently a minor issue, can sometimes signal a more significant underlying health concern. This common discoloration results from various factors, ranging from everyday injuries to rare but serious conditions. Understanding the potential causes and knowing when to seek professional medical advice is important for appropriate care.
Understanding What Causes Black Toenails
The most frequent reason for a toenail to turn black is trauma, leading to a subungual hematoma, a bruise under the nail. This occurs when blood vessels beneath the nail plate rupture due to an impact, such as stubbing a toe, dropping a heavy object on the foot, or from repetitive pressure. The blood collects under the nail, appearing black or dark purple. Athletes, particularly runners, often experience this due to repeated microtrauma from their toes hitting the front of their shoes, known as “runner’s toe.” The discoloration from a subungual hematoma resolves as the nail grows out over several months.
Fungal infections, though more commonly yellow or white, can cause toenails to appear black. Darkening can occur due to debris buildup or changes in nail pigment caused by fungi. Fungi thrive in warm, moist environments, making toenails susceptible, particularly within shoes. If left untreated, fungal infections can lead to nail thickening, crumbling, or even separation from the nail bed.
A rare but serious cause of a black toenail is subungual melanoma, a skin cancer developing under the nail. Unlike a bruise, subungual melanoma often appears as a dark streak that runs the entire length of the nail, may widen over time, and occurs without known injury. Other signs include discoloration extending to the skin surrounding the nail (Hutchinson’s sign), nail splitting, or the development of a nodule or bleeding. It can spread if not detected early. Less common causes include certain medications, underlying health conditions like diabetes, kidney disease, autoimmune disorders, and nutritional deficiencies.
When to Seek Professional Medical Advice
While many instances of black toenails resolve on their own, certain signs warrant a visit to a healthcare professional. If the discoloration appeared without known trauma or injury, or if it presents as a dark streak running the entire length of the nail, evaluation is needed. These may indicate serious conditions like subungual melanoma.
Persistent or increasing pain, swelling, or signs of infection around the nail, such as redness, warmth, pus, or discharge, require attention. Consultation is also advisable if the black spot spreads, changes size or color, or if the nail lifts or separates from the nail bed without clear traumatic cause. If the black toenail does not improve or grow out over several months, or if you have underlying health conditions like diabetes, professional advice is recommended.
What to Expect During Diagnosis and Treatment
When seeking medical advice for a black toenail, a professional will begin with a visual inspection of the affected nail. They will also ask about recent injuries, activities, and footwear habits to determine the cause. If a subungual hematoma (blood under the nail) is suspected, they may inquire about the timing and nature of trauma. In some cases, an X-ray may be performed to check for underlying bone injury, especially after significant impact.
For suspected fungal infections, a nail clipping or small sample may be taken for laboratory analysis. If subungual melanoma is a concern, especially with suspicious streaks or nail changes, a nail bed biopsy may be performed. Treatment depends entirely on the underlying cause. For painful subungual hematomas, a procedure called trephination may be performed, where a small hole is made in the nail to drain trapped blood and relieve pressure. This procedure is most effective within 48 hours of injury and is not painful as the nail lacks nerves.
Fungal infections are treated with topical (creams, polishes) or oral antifungal medications, depending on infection severity. Treatments may require several months to be effective as the infected nail grows out. In cases of subungual melanoma, surgical removal of affected tissue, possibly including the nail, is required. Further treatment may involve referral to an oncologist.
Steps to Prevent Black Toenails
Preventing black toenails involves simple measures focused on foot care and appropriate footwear. Wearing properly fitting shoes is a primary step, especially for athletes or those with repetitive foot impact activities. Shoes should have ample room in the toe box, allowing toes to move freely without rubbing against the shoe. A thumb’s width of space is recommended between your longest toe and the shoe’s end.
Trimming toenails correctly also prevents them. Nails should be cut straight across, not too short, and avoiding rounded edges to prevent ingrown nails and trauma. Regular trimming ensures nails do not extend past the tips of the toes, reducing impact against footwear. Protecting feet from direct trauma, such as wearing steel-toed boots in hazardous environments, also prevents injuries leading to black toenails.
Maintaining good foot hygiene, including keeping feet clean and dry, helps prevent fungal infections that can discolor nails. Moisture-wicking socks further assist in keeping feet dry, particularly during physical activity.